Installing an Underground Sprinkler System

An underground sprinkler popped up to water a lawn.

If you have spent thousands of dollars on landscaping, and live in an area of uncertain rainfall, you might consider installing an underground sprinkler system. Although not a job for the casual do it yourselfer, the job can be accomplished if the plan is well thought out and you take the time to investigate the needed steps.

Sprinkler System Design

Installing an underground sprinkler system should address these concerns:

  • Your watering needs — do you have lawn, shrubs, trees, and water beds to irrigate?
  • Is your lawn flat, or does it slope downwards?
  • Is your lawn small or large? Square or irregularly shaped?
  • Does your community have regulations on watering?
  • Do you have the skill sets to design and install an underground sprinkler system?

Lawn care experts strongly recommend that the design of the system be handled by a professional designer. The designer takes into consideration the layout of the property, placement of sprinkler heads, and what equipment is needed to drive the system. Some companies that design the systems will charge a fee but will credit back all or part of the fee towards purchase of parts.

TIP: Our expert gardening advisor, Rachel Klein recommends, "Keep sprinklers a minimum of 18 inches away from the walls of your home. If you live in a windy area, you may want to keep them up to five feet away from the house to prevent water stains."

Before beginning any digging or installation, check with city codes to insure there are no restrictions on water usage, and whether or not any underground cables or pipes will be affected by your installation. This information can be had from your local Department of Works.

Once the plan is in place, and you have checked city codes, the installation proceeds as follows:

  • Determine the flow rate of water in your home.
  • Tap into the water main of your home.
  • Build the distribution manifold for pipe connection.
  • Lay out the pipe.
  • Attach the sprinkler heads.
  • Test the system.

The Details

Determine Flow Rate

You need to know the flow rate of your home's water system to determine if it can handle the sprinkler system. Flow rate is the rate at which water flows from a source, i.e. your home. It is measured in gallons per minute. A cheap water pressure gauge can be bought at most hardware stores that sell lawn sprinkler systems. Or you can determine the gpm yourself by turning on an outside faucet fully, and counting the number of seconds it takes to fill a one gallon container.

Divide 60 by the number of seconds it takes to fill the container. This gives you the number of gallons per minute your home water system will produce. For example, if it took 20 seconds to fill your gallon, your gpm is 3 (60/20). Most sprinkler heads require a flow of 2 to 8 GPM to cover an 80-foot area of lawn.

TIP: Rachel Suggests, "If you don't have a one gallon container, fill a plastic bucket with 16 cups of water, and mark the water line with a black marker. This is one gallon. Have a stop watch ready for an accurate measurement, and record the number of seconds it takes to reach the line or to fill the container."

Tap Into Water Supply

Once the GPM is determined, you will then tap into the water supply using a tee.

TIP: Rachel advises, "In cold weather climates, the water supply should be tapped indoors, ideally in the basement or in a heated crawl space. In warm weather climates, outdoor pipes can be tapped."

This can be accomplished in three different ways:

  • Right after the water meter in your home, just past the water meter, cut into the line and install a compression tee.
  • Behind an outdoor water bibb.
  • On the main water supply line before it enters the home, but past the water meter.

Don't forget to turn off the water supply to your house before you get started.

TIP: Rachel recommends, "Even though you have smartly shut off the water to your house before cutting any pipes, it is a wise idea to position a bucket under the pipe before cutting to catch any water still caught in the pipe."

Next, install a stop and waste valve, which acts as an emergency shut off and a way to drain the system for the winter months. This valve will be installed just past the tee connection to the water supply.

TIP: Rachel cautions you, "Tapping into your water supply is a part of installation that may merit calling in a professional. Making a mistake with your plumbing system can be extraordinarily expensive to fix."

Install the Distribution Manifold

The main supply will be attached to the distribution manifold of the system. The manifold consists of a piece of PVC pipe with control valves installed 3 to 6 inches apart. Install an anti-siphoning device, a fail-safe check valve that is used to prevent water from contaminating the main water supply, to each control valve.

Typically, it is required on municipal systems. Each control valve will be driven by the controller, an electronic device usually installed in the garage. The distribution manifold can be buried in the ground with the control valves made accessible. Cover the installation with a box to prevent damage to the control valves.

We are now ready to proceed with the installation of the sprinkler system its self. On to Part 2.