How to Check Sprinkler Water Flow GPM

Water flow rate is commonly checked at the source by timing how long it takes to fill a bucket and then calculating gallons per minute. You can also check at the source or along pipes using a flow meter that threads onto a connection.

Water flow, similar to water pressure, is vital for making sure your sprinkler system is running at its maximum efficiency and putting out the amount of water it should.

What is water flow rate?

Water flow rate is the volume or quantity of water moving through a pipe or irrigation line over a specified time. Usually, it’s expressed in gallons per minute (GPM), but in irrigation systems (e.g., sprinkler heads or emitters), it is often described as gallons per hour (GPH).

What is the difference between water flow and water pressure?

While the two are related to one another, there is a simple way to express the difference between water flow and pressure.

  • Water flow is how much water is coming out of your system through the pipes.
  • Water pressure is how hard this water comes out of the pipes.

In general, the higher the water pressure, the greater the water flow since more pressure can force more water through the system. The lower the pressure, the lower the water flow.

What is the ideal sprinkler water flow GPM?

For an Irrigreen smart sprinkler system, you need at least 8GPM water flow at your source. If it’s less than this, your system will not work correctly or as efficiently.

Most other traditional and smart sprinkler systems have similar minimum GPM requirements.

Problems with low flow rate

A low flow rate causes problems similar to low water pressure. The biggest issue you’ll see is a significant drop in sprinkler efficiency. When the flow rate is low, your sprinklers may not have enough water moving through them to pop up and fully seat, and the output will be reduced.

Problems with high flow rate

The biggest problem with a high water flow rate is an issue called scrubbing. It’s essentially the gradual wearing away of the inside of water lines or pipes, typically one molecule at a time.

You’re probably thinking, how does clean water damage the inside of pipes? Plain and simple, water is abrasive.

Let’s think about it in another way. For instance, look at how moving water in a river wears away at a stream bank over time. The faster the water moves, i.e., during spring runoff, the more it cuts into the bank, widening the stream bed.

There’s a similar phenomenon happening inside your pipes. Even when the water doesn’t have any particulates in it, it’s wearing away at them. When water moves through your pipes at a high velocity, it slowly scrubs away the inside, changing the inner diameter.

As it moves faster, the scrubbing gets worse and can wear down the pipe wall to the point it’s so weak it splits. This issue is less problematic in plastic or PVC pipes because of the slicker surface, but it still occurs.

Measuring sprinkler water flow GPM

The easiest way to measure how much water comes out and how quickly it does so is by conducting what is known as the bucket test. All you need is a 5-gallon plastic pail and a stopwatch.

Place the empty plastic pail beneath the hose spigot, turn on the water at full pressure, and start the stopwatch at the same time. When the bucket is full, note the length of time it took. You can then calculate the water flow in GPM.

Number of gallons / Bucket fill time in seconds X 60 seconds = Gallons Per Minute

For example, it took 36 seconds to fill a 5-gallon bucket.

→5 gallons / 36 seconds = 0.14 gallons per second

→0.14 gallons per second X 60 seconds per minute = 8.4 gallons per minute (GPM)

You can also use a flow meter, which is similar to a pressure gauge used to measure water pressure. A flow meter attaches to the hose spigot, and when turned on, it measures how much water moves through it, calculating gallons per minute.

A water flow meter can also be used to measure water flow at specific points in your irrigation supply line as long as the connection size matches. Many meters have a 1” connecter, so you can thread it onto a 1” PVC line to see if you’re losing water flow between the source and somewhere downline.

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