Your garden should be one of the best features of your home. Even the most beautiful modern house will seem sterile and gloomy if it’s surrounded by nothing but weeds and dust.
Water makes all the difference here and, unless you’re lucky enough to live in an area with plentiful year-round rain, this generally means installing a sprinkler system of some kind.
You can, of course, do all of your watering by hand. However, this means spending hours each week dragging a hose around, lots of wasted water, and the chance of your plants wilting and dying if you can’t get to them for a while.
A well-planned irrigation setup neatly solves all of these problems. It’s probably going to be fairly expensive to install, though, so make sure you have all the information you need before you start laying pipe. This guide is designed to help you with exactly that.
- Irrigation by Design: Gardens Don’t Plan Themselves
- How Landscape Architects Approach Irrigation (and How You Can, Too)
- First Things First: Pressure and Flow
- How Big is Your Garden Really?
- Slopes, Soil, Species, and Sun
- Positioning Your Sprinklers
- Overview of The Parts that Go Into Making an Irrigation System
- Plugging in the Numbers
- Dollars and Sense
Irrigation by Design: Gardens Don’t Plan Themselves
Getting from this …
… to this …
… is certainly not the easiest task in the world.
At first, you will probably get a real thrill from allowing your imagination free rein, but soon enough you’ll run up against some hard realities. All plants won’t grow well or even survive in every climate zone; your soil type may not be adequate for what you have in mind, and the time and funds needed to realize your vision may just not be available right now.
Planning a garden is therefore all about finding the best possible compromise between your horticultural dreams and your resources. Crucially, aside from layout and plant selection, designing an efficient irrigation system is a large part of this.
Think of it this way: plants basically need dirt, sunlight, and water – only one of these is really under your control.
How Landscape Architects Approach Irrigation (and How You Can, Too)
Every profession has its conventions and jargon. Sometimes, these are used to confuse customers:
“I’ll need to recalibrate your dingaloo, replace your rombomber and floopdidoodles, and rebuild your fotzpitz.”
“Do front-wheel-drive cars even have fotzpitzes?”
For the most part, though, shorthand words are used because they make things clearer, not more obscure. People in the same trade also share some unspoken assumptions that aren’t always clear to outsiders.
Almost all builders start a building at its foundations; working from the roof down would be weird and silly. For their part, most full-time landscapers will think about things in the following order when designing an irrigation system:
- The water source,
- Terrain, climate, and local weather
- The plants’ water requirements,
- The actual positioning of the sprinklers and layout of the pipe network,
- Installation and materials budgeting.
When you follow this step-by-step program, you’ll never have to ask yourself: “What now?”.
It works equally well for planning a totally new system or tweaking an existing one. Mistakes and oversights are much less likely when you have a framework like this to guide you through the process.
We’ll be covering each of these aspects in detail down below, hopefully answering any questions you have along the way. Some of these preliminaries may seem tedious, but they’re definitely worth knowing about.
We might as well take this opportunity to point out that the last part – figuring out what everything will cost – is often where expectation meets reality, painfully. You may have to settle for a smaller installation than you originally had in mind and plan for it to accommodate future upgrades or expansions. When it comes to sprinkler systems, you can generally expect to pay between $0.25 and $1 for every square foot covered, and trying to save money by cutting corners is rarely a good idea.
On a closely-related note, you’ll have to be honest about your DIY skills and the amount of time you’re willing to put into this project. If you’re unsure of either, it might actually be cheaper to pay for professional, hassle-free installation.
First Things First: Pressure and Flow
Regardless of how much money you spend or how carefully you position your sprinklers, your garden will not be watered correctly if you neglect to take these two factors into account.
Their meanings are pretty much what you’d expect. The flow rate is the maximum amount of water that can be delivered to your garden at any one time, while the pressure is the “push” that allow your sprinklers to spray water over an area instead of just dribbling it into a puddle.
An insufficient flow rate or a pressure that’s too low will limit your choices with regard to which sprinklers will work effectively. It can also lead to insufficient watering if you run too many sprinklers on the same pipe:
As we’ll get to in a little while, the type of pipe you use and the distance between the supply and the sprinkler head also play a major role.
Pressure (or Lack Thereof)
The pressure in those big concrete pipes used for water distribution is typically around 10 bar (150 psi), which is enough to dig an impressive crater when one bursts. This level is reduced in a number of ways before it gets to your house and varies considerably between different properties, so it’s important to get an idea of what you have to work with.
One way to determine your water pressure is to simply phone up the utility company and ask for your neighborhood’s “static” pressure. However, especially if you live in a hilly area, this may be fairly inaccurate – a rise of only 30 feet changes the pressure by almost 15 psi – so it’s better to use a cheap pressure gauge to get an exact reading. Remember to check this at ground-floor level, again because water pressure varies with height. Also make sure that all the taps in the house are closed and the dishwasher isn’t running: pressure drops as flow rate increases.
Any reading between 50 and 60 psi should work well with a sprinkler system. You may want to install a pressure regulator if your water pressure is higher than this, if only to save the inlet valves on your domestic appliances from wear and tear. If your pressure is significantly lower, you can consider buying a pressure booster pump – you’ll probably save more than what the pump costs due to the way adequate pressure simplifies the overall sprinkler system design.
Let It Flow
There are basically two ways of determining your maximum flow rate in Gallons per Minute (GPM).
The first is pretty simple: find a 5-gallon bucket and time how quickly you can fill it from the tap to which you connect your garden hose. Then use …
… to determine your maximum GPM figure.
The second method is even simpler. Just find the narrowest pipe between the point where the utility company’s pipe enters your property and where you plan to connect your sprinklers. Measure its width with a ruler and look up the corresponding number in this table:
If the pipe in question is less than 5′ long, you can probably ignore it, but it pays to be conservative here (or more accurately: being too optimistic can be expensive). The flow rate you will use for your sprinklers is the lower of the two numbers: sometimes, just because you can push the limits doesn’t mean that you should.
Although we don’t normally think of water as something that can scour away plastic or metal, this does happen, albeit slowly. If you exceed what the pipes are designed to handle, you’ll have to replace them that much sooner.
The other problem with excessive flow rates is called “water hammer”. A ½” column of water 100 feet long weighs 340 pounds. If it happens to be flowing at a rate of 12 GPM, it has approximately the same amount of energy as a baseball flying at 300 miles per hour. An electronic valve, like those commonly found in irrigation controllers, shuts off almost instantly, leaving all that energy with nowhere to go except smack into that valve, the joints in your plumbing, and whatever else is likely to burst.
In other words, it’s really better to accept a safe GPM number for your sprinklers than to flood your basement on a regular basis.
Being careful when estimating the amount of water available to your sprinklers has a further advantage. As can’t be said often enough, the pressure you actually have available to work with drops off as water flow rises. Trying to jack up your GPM figure may leave you with too few psi to get the job done.
How Big is Your Garden Really?
The number you have for your maximum flow rate is pretty meaningless if you don’t know what surface area you’re going to be watering, preferably as precisely as possible. You don’t need to know the length and breadth of your garden to a fraction of an inch, but you should at least use a measuring tape or wheel instead of guessing.
The reason this is important is the following formula, which you’ll be referring to more than once while designing your ideal irrigation system:
If you don’t know how large each area you want to water is, you’ll probably end up using too few or too many sprinklers, leaving patches of ground either perpetually dry or soaked. Both of these conditions are likely to kill your plants.
It’s highly recommended that you get some graph paper and draw a sketch as you go along, even if this is only so you have something to show to a landscaper or at the plumbing supply store. It can look as simple as this:
While you’re at it, also mark down any changes in elevation, as this will have a significant effect on your water pressure at any given point.
Slopes, Soil, Species, and Sun
Now that you know how much water you have available in terms of GPM and how much ground you need to cover with it, it’s time to make some preliminary decisions on how you’re going to allocate that water. More specifically, you’ll want to save as much as possible while making sure your plants get the irrigation they need to thrive.
Getting from Flow Rates to Foliage (Example)
You can use the following table as a starting point (note that “Climate” refers to the typical humidity here):
As a general rule, you can divide these numbers in half for shrubbery and herbaceous borders, while flowerbed needs depend heavily on the actual plants species and other factors. You’ll also have to make a guess on whether to adjust the figure up or down depending on how much shade a given patch receives, how windy it usually is, and so forth. Knowing exact local weather figures certainly helps.
The reason for this is, of course, evaporation. A lot of irrigation water is lost before it even reaches the soil, baked away by the sun or blown off course by the wind.
You also have to take into account the soil composition in your yard: coarse, sandy soil drains very quickly and plants growing in it will benefit from frequent, brief waterings. Clay, on the other hand, retains a lot of water, making overwatering (and consequently, root disease) a real risk.
Representative “infiltration rates” – how fast water sinks below the surface, saturating the soil as it goes – are:
None of these numbers should be taken as gospel, but they are a useful planning tool.
Taking the lawn in our drawing above as an example, we have 200 square feet in total to take care of. Assuming that we live in an area with moderate humidity and an average day temperature of 70°F, our grass should need about 1.8″ of water per week. Let’s assume a flow figure of 6 GPM for the sprinkler system, so we end up with …
… and a total watering time of about 38 minutes per week.
We also don’t want too much water to flow off the turfed area. Looking at our soil type table, we see that we can expect our relatively dense soil to absorb only about half an inch of water per hour. If we split our 38 minutes and 1.8″ of watering into two sessions per week, it works out to 0.9″ in 19 minutes (2.7 inch/hour), which is too much – turning on the sprinklers for a shorter period every day will reduce the amount of runoff and stop the ground from getting waterlogged.
Remember that how fast your soil can absorb water is determined not only by its basic type, but also by its quality. Clay that contains a large amount of organic material will drain more quickly, while sandy soil with some compost mixed in will retain water better.
How Terrain Influences Irrigation Decisions
You’ll have noticed by now that this guide places a lot of emphasis on water pressure and its cousin, flow rate. This is not an accident: understanding these can make the difference between a design that works flawlessly and one that barely functions. This is always important, but doubly so if your plot is located on a hillside.
Water is heavy. The more of it that’s stacked on top of itself, the more forcefully it presses down.
What’s important to know here is that, in a pipe filled with water, the actual amount of water and the shape of the pipe doesn’t matter when it comes to static (i.e. non-flowing) pressure. All that counts is how far one point is above or below another.
Let’s say your water pressure at the house main is 40 psi and you have one sprinkler 10 feet vertically below with another 10 feet vertically above that point:
Every foot difference changes the water pressure by 0.433 psi. This means that sprinklers on the lower lawn will actually receive 44 psi, while the ones above them will have to make do with only 36.
When combined with other sources of pressure loss, this can make a pretty big difference and has to be accounted for. In particular, you will want all sprinklers or emitters on the same branch line to be at approximately the same height.
Steep slopes, especially clay-rich ones, are also more conducive to runoff, or water that flows away from where it’s needed before being absorbed by the ground. If you don’t want to waste water and potentially lose topsoil, it’s a good idea to irrigate inclined areas for several brief periods rather than one long session.
Programmable sprinkler systems make this easy. Rotors or rotating sprinkler heads also work better on these surfaces: some fixed sprayers tend to deliver water to the same spots continuously without giving the soil a chance to soak it up between passes.
The type of soil and climate you have in your region also affect what kind of piping you’ll install. If your yard is especially rocky or your winters harsh, investing in a higher grade of pipe such as PEX can save you the grief of having to dig up half your lawn to find and repair a leak. If the ground freezes down to a couple of inches deep, it’s recommended that you use piping rated for double the normal operating pressure, even assuming that you’ll drain or blow out the water lines come fall.
Positioning Your Sprinklers
At this point, we have enough information to begin where many irrigation amateurs would have started: actually deciding where the sprinklers should go. In most gardens, you’ll find some or all of the following types useful:
- Impact Rotors: Known for their characteristic “twop-twop” sound, rotors work well for watering large spaces. They require a relatively high pressure to operate and, unlike pop-up spray heads, can’t be concealed.
- Spray Heads: Available with different nozzles, including rotating ones, these are less noisy and an efficient way to cover smaller or irregular spaces. They typically operate at lower pressure levels.
- Drip Emitters: Very water-efficient, these deliver low-pressure water slowly and directly to the base of the plant. You can also find high-flow drip irrigation systems intended to flood small areas in a short amount of time, called “bubblers”. These may be useful in some situations, like when watering planters, but are more of a speciality item you can easily do without.
We’ll be talking mainly about spray heads in what follows, but you’ll be able to adapt what you read to impact rotors or drip irrigation without any trouble.
More About Sprinklers
All sprinklers come with a triad of three variables: pressure, distance, and flow rate. It’s of absolutely no use to be told simply that some model “sprays up to 12 feet”, you also need to know how much pressure this requires and how much water is dispensed.
This information is usually given as a table, e.g. a given sprinkler head might cover an area 12″ in radius at 30 psi and use 2.4 GPM while doing so, with corresponding values for other pressures. If the manufacturer can’t supply you with this information, you should probably not be buying from them in the first place.
Spray heads that each cover a larger area tend to be more expensive individually, but also require less trenching and piping. In the end, the total budget works out about the same, so the kind of sprinklers you select will come down mostly to what level of pressure you have to work with and the kind of areas you need to water. Wherever possible, you’ll probably want to use pop-up sprayers in your garden; they don’t really cost any more than those mounted on a permanent riser and are more likely to survive interactions with gardening tools and dogs.
On most sprinkler heads, you can adjust the spray radius using a screwdriver without reducing the pressure in the zone as a whole. You can also install a nozzle designed to give a smaller spray radius, angle, or flow rate (adjusting a 4 GPM sprayer to cover only a 90° arc doesn’t necessarily cut its watering rate to 1 GPM). This comes in handy when a large space has a few awkward corners.
While we are on the topic, there’s nothing wrong with installing outward-facing sprinklers as far as half a foot away from walls or paving. Almost all sprinkle some water in their immediate vicinity. This isn’t a design defect, but something that allows you to place them where lawn edging tools won’t damage them.
Important Sprinkler Positioning Tips
Generally, you’ll probably want to use rotors or rotating spray nozzles to cover large areas like lawns while servicing smaller spaces with fixed sprinklers. The map you’ve drawn while measuring your garden will be invaluable here: actually pencil in the position of different sprinkler heads along with their coverage areas. You’ll probably have to make several attempts to get this right, but it’s well worth it (and you thought you’d never use the geometry you learned in high school!).
For the moment, just choose a popular general-purpose sprinkler and determine its spray radius using the pressure value you measured before, minus 10 psi – we’ll refine this figure shortly.
One thing that’s important to remember here is that you have to minimize the size of any dry spots, even if this means that most areas receive water from more than one sprinkler. Contrary to what you’d expect, this actually saves water: though parts of your lawn or beds will be overwatered slightly, this moisture spreads out to some extent both above and below ground. At the same time, you don’t need to over-water almost all of your lawn just to get to the poorly watered, withering areas.
These three images clearly illustrate this:
It’s tempting to save money by using fewer sprinkler heads, but this can easily end up being a false saving. No sprinkler waters the entire area within its radius evenly. The only way to compensate for this and ensure that your whole lawn gets saturated is to confirm that the water from each sprinkler head reaches its neighbors. If this doesn’t happen, it’s very likely that you’ll see a noticeable difference in appearance between one patch of grass and the next.
Overview: The Parts that Go Into Making an Irrigation System and How They Fit Together
Up until now, we’ve been speaking about sprinklers, pipes, and so forth in pretty general terms. If you’re reading this, after all, you probably have a pretty good idea about what a sprinkler system is and more or less how it works.
Before we get to the next section, though, it makes sense to set out exactly what route water follows from A to B and what’s involved at each step. Once we’ve done that, figuring out what the actual pressure at each sprinkler head should be will be a lot simpler. Here’s the schematic overview:
Point of Connection (1)
“POC” is a pretty common term in the landscape industry. It simply means “where the sprinkler system is hooked up to the main water supply”. This is an important concept. Ideally, you’ll hook up your irrigation mainline to that of the house (the house mainline is the tube between your water meter and where it enters the building). This provides the greatest amount of flow and pressure, which is handy as your sprinklers will likely be a lot thirstier than a shower or faucet.
Especially if your water pressure or flow rate isn’t the best, connecting your irrigation system as far upstream as possible can prevent a number of problems. Nobody wants to be woken up by gurgling indoor pipes when the sprinklers switch on at 3am, while water being forced through a whole bunch of indoor plumbing not meant for irrigation volumes will wear out your pipes that much sooner. In case you need to do maintenance or repair a leak, you should install an emergency stop valve at this point.
The irrigation mainline is the portion of pipe running between your POC and wherever your zone valves are located. Since this section is usually short, affects your irrigation pressure everywhere, is subject to water hammer from downstream valves, and will shut down the whole system if it bursts, a high-quality tube a size or two larger than whatever pipe feeds into it is commonly used here.
Filter and Backflow Preventer (3)
Most automatic valves are sensitive beasts, and your water supply probably contains more grit than you realize. Installing a particle filter of between 100 and 200 mesh costs little and will keep your valves and sprinkler heads running smoothly for much longer. A filter is an absolute must if you’re planning on using drip irrigation.
A backflow preventer stops irrigation water that potentially contains traces of fertilizer, manure, and other nasty stuff from flowing upstream and contaminating the municipal supply. Putting one on your irrigation mainline is often legally mandated to protect potable water sources. These regulations, including which types of backflow preventers are considered adequate, vary from place to place, so your best bet is to ask at your local plumbing supply store.
Understandably but somewhat annoyingly, all parts of your system upstream of the backflow preventer are considered part of the house’s plumbing (as are any tubes running through the building), so you’ll have to take local building codes into consideration and select pipes that meet these specifications. In many locations, you actually have to apply for a permit to install a sprinkler system. Make sure of this before you start, or you may be faced with the hassle of tearing out and re-doing a large portion of your work.
Whether manual or automatic, it’s usually most convenient to install these in groups, perhaps using a manifold to keep things tidy and organized. Since these allow water from the pressurized, large-bore mainline into the narrower pipes servicing each zone, it’s a good idea to locate them fairly close to the actual sprinklers to conserve pressure. You could, for example, have one cluster of valves servicing the front yard and another for the back, both connected to your irrigation mainline.
Most new irrigation systems utilize a computerized controller; these cost little compared to the rest of the system and make it twice as convenient to use. Pretty much all automatic valves intended for household use are controlled by a 24 volt a.c. current, so you can mix and match manufacturers to your heart’s content.
Some electronic valves also have a manual setting, meaning that you can close it if it should fail in the open position. More importantly, this allows you to adjust the amount of water it lets through, making it easy to tweak a zone if the sprinklers it controls are getting too much water.
Other, more expensive models include more accurate pressure regulators, or you can buy a separate regulator (5) if need be. This will probably be the case if you want to use drip irrigation (6).
Valves are designed with widely different purposes and characteristics. Some, like those you might use on a drip line, work just fine at flow rates well under 1 GPM, while others require a much higher minimum flow and/or pressure to open and close properly.
Water lines branching off your irrigation mainline are called “laterals”. As you will soon see, choosing the right diameter pipe for these is one of the most important design decisions you’ll have to make.
If you’re not using a professional landscaping company to install your system, however, this choice may be simplified. It’s very likely that using the same type and gauge of tubing for all the pipes leading to individual watering zones will work out cheaper, as you will be buying an entire roll instead of per foot. It’s up to you to do the math, but it’s worth remembering that using a larger-than-necessary pipe almost never causes problems and may keep you from running into a few.
Since lateral tubes are typically buried at least 10″ under the surface for protection, some kind of piping is needed to connect them to the sprinklers they feed. These are called risers. Their most important characteristic is that they should ideally be flexible in order to make damage to the sprinkler head or branch pipe less likely. This also allows you to place sprinkler heads a short distance away from the pipe’s route.
There are specialist products available for this purpose, but any kind of flexible pipe of the same size as the sprinkler head intake will do. Installation will take a little more time (with a correspondingly greater chance of screwing something up), but adding your own fittings to a length of pipe you cut yourself will generally work out a little cheaper.
Assuming you’ve read this far, you almost certainly know what a sprinkler is, what they look like and what they do. If you need a quick refresher on some of the most common types, here’s a video for you:
Even if you have a good general idea of what kind of sprinkler heads you need, it can still be worth spending half an hour in a hardware store to see what’s available. Specialized products like sidestrip heads and misters often neatly solve an otherwise intractable problem.
Plugging in the Numbers
If you’ve worked through our guide up to this point, you have reason to feel pretty good about yourself and the irrigation system you’ve designed. Will it work, though? The hard way of finding out is to install the whole thing, turn it on, and see. The easy way involves a little bit of math.
A hydrozone is simply any area you’ll water in the same way. Usually, each hydrozone’s sprinklers are all connected to the same valve, forming a valve zone.
This situation is so common that the word “zone” can be used to refer to either a hydro- or valve zone, for the most part without any confusion. You will generally lay out your garden so that plants with similar water requirements are clumped together, but you can also try little tricks like superimposing two valve zones on the same area. You might, for instance, want a sprayer zone to take care of a hardy groundcover and combine this with a drip irrigation system to support more water-hungry shrubs.
It’s a good idea to use only identical sprinklers in each valve zone, since even small variations in spray patterns and flow rate/pressure characteristics can throw off the most careful calculations. Combining different models willy-nilly will frequently result in some areas getting waterlogged while others remain nearly dry.
If you’ve already drawn a diagram showing sprinkler positioning, it should be easy to see which sprinklers cover areas with similar water needs and are also close enough to run on the same pipe. These naturally fall into the same valve zone, unless their total projected flow rate is higher than the maximum you determined earlier. If this is the case, simply split the zone in two.
Friction Pressure Loss
We’ve previously measured the water pressure at your point of connection with no water running; this is called your static pressure. As soon as a fluid starts moving through a tube, valve or other conduit, though, the operating pressure starts to drop off.
When it comes to tubes, the most important variables are the pipe’s width, its length, and the speed of the water inside. There are a number of online calculators to help you estimate how much pressure will be lost in a given pipe (or, conversely, how large a pipe you need to keep these losses within defined limits). You’ll have to account for every section of pipe between your water meter and sprinkler head: the most restrictive one will usually be the limiting factor.
For components like water meters, valves, and filters, the only way to estimate their associated pressure loss at a given flow rate is to look through the manufacturer’s documentation. As a very rough guide to help you in the initial planning stages, you can use the following table. We have to emphasize this: unless you have tons of pressure to spare, you should really find exact information about every part in your system, or risk your sprinklers not working properly.
To find the total pressure loss, the numbers for every component or pipe water passes through on its way to its destination are added together.
Note: Remember that pressure losses become larger as flow rate increases! The more water is drawn through the mainline at any one time, the less power will be available to each sprinkler.
Too much pressure is rarely much of a problem. If need be, all you need to do is connect a cheap inline pressure regulator and you’re good to go.
Pressure that’s too low, on the other hand, may mean having to spend significantly more money, changing your irrigation design completely, or both. While you should check the data sheet of whatever sprinker heads you plan to buy, the numbers this gives will probably be comparable to these:
The amount of pressure you have available will therefore limit your options as to what types of irrigation you can install.
Another important consideration here is that pressure loss within a branch line should be no more than 5 psi, or sprinklers near the valve will spray much more than those located at the end:
This can be rectified to some extent by adjusting the flow rate on individual spray heads, but using a larger pipe is a much better solution – if the pipe is too narrow to begin with, you may have to dig up the whole shebang and start over.
Time for Some Math
Short of actually digging trenches and installing the pipework, the following step constitutes the biggest task involved in creating a new irrigation system. Although it can be tedious, it really is important to calculate the water pressure at every single sprinkler head, or your results may turn out to be sub-par.
The reason this can get frustrating is that it’s often an iterative process; in other words, you might have to go right back to the drawing board several times until you get to a setup that will work in terms of cost, pressure and flow, and, of course, actual watering performance. You might, for instance, have to go through the entire process again using a different model of sprinkler head with a lower flow rate, or specify a wider pipe for your lateral lines.
The easiest way to illustrate how this works is through an example. Let’s say the system below is fed from a 40 psi source capable of delivering 20 GPM.
The sprinklers’ performance is given by the manufacturer as follows:
The lateral pipe is made of polyethylene and its diameter is ¾”. For simplicity, we’ll say that all 5 sprinklers are at the same height, so we don’t have to take that 0.433/foot factor into account. If they were not on a level surface, we’d simply add or subtract the appropriate amount from the pressure at each sprinkler when we calculate it.
Now, rounding off a little, we can guess that the total flow through the zone valve will be around 12.5 GPM, taking the highest likely figure to be safe (2.5 GPM times 5 sprinklers). Using this number and adding together the expected pressure losses upstream of the lateral – the solenoid valve that turns it on and off, the filter and backflow preventer, the mainline pipe itself – we see that we can expect 7 psi less than the original static pressure of 40 psi at the start of our branch line.
We could recalculate the branch line’s flow rate again based on this new pressure value, but the difference is negligible (and we want to have a safety margin anyway). Let’s focus instead on how the length of each pipe segment affects the effective pressure at the different sprinkler heads:
Using an online calculator, we can easily calculate the losses caused by each pipe segment:
Now we see that the last sprinkler receives somewhat less pressure than the first, affecting not only its total spray radius but also the water distribution within that area. On a lawn, for instance, this really isn’t what you want, but in this case the variation is acceptable (less than 5 psi).
If the pressure drop were much greater than that, we could use a larger pipe, choose another type of sprinkler head or re-route the tubes into a “star” configuration, which would decrease the total distance water has to go to reach the final sprinkler. In any case, you should be glad if you found a potential problem through this exercise: discovering the same thing by half your lawn dying off is much less pleasant.
Dollars and Sense
The final step in designing an irrigation system for your garden is figuring out how much it will set you back. Many people try to do things back to front, in other words ask “How much can I get for what I’m willing to spend?” This may seem like the logical approach, but the problem is that most of us will quickly succumb to the temptation of adjusting the project to the budget instead of the other way around. Since the typical home sprinkler system will see a decade or more of use, it’s most definitely a good idea to get it right, even if this means not getting what you want right now.
On a closely-related note, using low-grade materials – piping with a maximum pressure rating less than twice what it will actually carry, cut-rate sprinklers, valves from a company you’ve never heard of – is almost always a mistake.
Established irrigation supply companies rely on contractors for half or more of their business. People that install and maintain sprinkler systems for a living obviously have a vested interest in using reliable products, so brand-name manufacturers have found that upholding a reputation for quality is far more important than making a quick profit. Buying something cheap often means having to buy it twice.
Paying in Sweat Instead of Money
The price tag for professional installation can often run to 300% of what it would cost to buy the parts yourself and put in the necessary elbow grease. This may seem like a great opportunity to save a lot of cash, but many DIYers fail to understand just how greasy their elbows will get.
While there’s nothing technically difficult about laying and joining pipes (and there are tons of free tutorials available on the subject), there’s a good reason for contractors charging the rates they do. A spadeful of wet dirt can easily weigh 15 lbs or more, for instance, while dealing with unexpected problems like inconveniently placed tree roots can take hours.
There’s also the peace of mind of hiring a professional. Can you make a leak-free plumbing joint 100% of the time? If the most you can realistically hope for is a figure of 90%, tackling any fairly large system will have you pulling out your hair in no time. The same goes for any of a number of small but crucial jobs: waterproofing electrical connections, flushing dirt out of the pipelines before installing the sprinkler heads, and lifting and replacing turf without the grass dying are all good examples.
Of course, like when hiring any kind of contractor it rarely hurts to ask for references and get multiple quotes. Also make sure that these are itemized with regard to materials: even professionals sometimes risk substituting cheaper materials in order to put in the winning bid. They should also be able to present an irrigation plan similar to the one this guide has shown you how to compile – if they claim they don’t need one because of their “judgment” and “experience”, it’s probably better to pass them by. There’s very little to stop any fool from calling himself a landscaping designer and setting up shop, so choosing a company with a proven track record is very important.
Thanks for Reading!
This guide contains quite a lot of information, much of which you probably haven’t seen before. If you’ve made it this far, reward yourself with a cookie (and send me one too).
The simple truth is that an irrigation system designed using a systematic approach will almost always outperform one which was more or less slapped together using a combination of intuition and wishful thinking. Working through this guide as it applies to your garden should take no more than two hours, but may be enough to save you thousands of dollars, especially if it prevents you from having to redo half of your sprinkler system after it’s already in the ground.
Measure twice, cut once!