Most people have no idea how much water they use to irrigate their lawn and garden until they receive that first, and often shocking, water bill of the summer. By doing some simple math you can avoid that annual shocker and obtain an understanding of your water use.

Let’s start with the basics -

In the world of irrigation, there are generally 4 types of  water delivery mechanisms; Rotor head sprinklers, Spray head sprinklers, Drip systems, and the good old fashioned garden hose.

Rotor (or oscillating) Heads

As the name implies, these sprinklers deliver water while rotating (think of the dance that inevitably shows itself at late night wedding receptions and shabby disco parties). These sprinkler heads can cover some distance while delivering a larger water droplet preventing excessive water loss due to evaporative misting and wind.

USE – Residential rotor heads generally use about 2.5 gpm. The further the spray, the higher the gpm.

Spray Heads

Spray head type sprinklers provide uniform distribution across your landscape. These are generally used in small or confined areas where a rotor head won’t work (think medians, raised planters etc). Their water delivery is generally a mist of small water droplets. As a rule of thumb, the smaller the water droplet (or finer the spray) the more water that is lost to evaporation and wind. That’s why rotor sprinklers are preferred in large, open areas.

USE – The individual nozzles can be changed out to achieve an ideal coverage of the area. These nozzles can deliver anywhere from 0.29 gpm for really small or tight spaces to 3.5 gpm for wider, open spaces.

Drip Systems

Drip systems are by far the most efficient form of irrigation for spot specific watering…like in your garden. A mainline hose (or pipe) is laid down and smaller emitters are punched into the mainline where desired. A small hose then delivers the water to the base of the plant. The emitters  then regulate the amount of water traveling to the plant. This allows for different water flows to plants with varied water needs. The slower, spot-specific water delivery ensures that very little is lost to evaporation, wind, or other factors while achieving good root saturation.

USE – Emitters are measured in gallons per HOUR (gph). The smallest emitters deliver about 1/2 gph while larger emitters will deliver 2 gph. The most common size is 1 gph.

The Hose

The garden hose is a versatile and foundational tool in any irrigation system. Its sleek and slender design design lends itself to kinking and twisting while the materials of constructions always make a long cool drink of water from the hose taste like…well…a hose. Not to mention its ability to cross over into other realms of workmanship like towing a car, becoming a drying line for clothes, or serving as a babysitter for your rambunctious kids. But seriously, hand watering plants and lawns with the hose allows for spot specific application of water at a high rate. A hose can go where an irrigation cannot (certainly some would argue differently. To those people, I would encourage them to start their own blog). This  makes the hose a very useful and necessary tool that no home should be without.

So…now that you know a little bit about the systems of delivery, let’s get into the math.

Take a walk in your yard and identify what type of sprinklers are present (rotor / spray / both / drip) and how may you have.

Next you need to figure out the gpm’s. Depending upon the make and model, some sprinkler heads will display the gpm right on top. You can also go online and get the info pretty easily (Try this one, or this one). The most common size issued in residential systems are 2 – 2.5 gpm.

Once you know the gpm’s and the number of heads the hard part is over! Let’s say you have 10 identical heads that all spray 2.5 gpm.  You now know that for each minute your irrigation system is on, you will use approximatively 25 gallons of water (10 heads x 2.5 gpm = 25 gallons per minute). Since you like your lawn lush and green and you’re not the type to waste water unnecessarily, you have the irrigation system timer set to turn on for a 2 hour cycle every-other morning before the sun comes up; that’s 120 minutes every-other day. 120 minutes  x 25 gallons per minute = 3000 gallons cycle.

Most water utilities bill in 30 day cycles, PAWSD is no exception.  When you get your monthly water bill, you now know that approximatively 45,000 gallons of your overall use is due to the irrigation system (120 min x 25 gpm x 15 days = 45,000 gallons).

Confused? Try this.

Nobody said a beautiful yard was cheap.

You can even take it a step further with your knowledge that the average American uses about 100 gallons of water per day. If you have, say, 3 people in your home, you can bet on about 300 gallons of use per day (remember, this is a national average, the same average that says US men weigh 191 pounds and stand 5′91/2″).

100 gallons per person per day x 3 people x 30 days = 9000 gallons.

Using the examples above, if your monthly water bill is in the 50,000 to 60,000 gallon range, there is no need for alarm. Should your bill be nowhere near the the ballpark figures you established…you probably have a leak somewhere and should address that as soon as possible. Call your local utility or plumber, they are there to help.