Part 1: Three Types of Irrigation Water

Did you know that there are three types of water that you can legally and safely use to irrigate landscape plants in California?

  • Potable Water
  • Recycled Water
  • Gray Water

The California Supplemental Exam for landscape architects includes questions about water quality and the different types of water that can be used to irrigate landscape plantings. As landscape architects, we are responsible to understand state and local codes, regulations, and ordinances regarding water usage. Avoiding water contamination and preventing the spread of waterborne illnesses is an important professional knowledge area where landscape architects can serve and protect their clients and the public.

In this series, we will review the three types of water that landscape architects can use to safely water landscape plants and conserve water in the process.

Much of the discussion in the series comes from the California Plumbing Code. The state’s plumbing code is usually adopted by local permitting authorities as the standard for safety and is widely accepted by the tradesmen.

Over the next few days, we will examine all three types of irrigation water. Today’s article focuses on potable water.

What is Potable Water?

Potable water is safe to drink for people and pets.

Photo by Elyce Feliz.

Potable Water is defined as water that is drinkable and meets the U.S. Environmental Protection Agency (EPA) Drinking Water Standards. Potable water is fit for human consumption and can be used for drinking water, bathing or showering, handwashing, oral hygiene, or cooking, including, but not limited to, preparing food and washing dishes.

Potable water systems must be kept completely separate from recycled water systems. To avoid the possibility of cross contamination, potable water and recycled water pipes cannot be laid in the same trench and must have 10 feet of horizontal distance separating the two water types. Blue is the color used to signify potable water systems while purple indicates a recycled water system. Continue reading for more information on recycled water systems.

Potable Water is a precious resource and the most environmentally expensive water to use in the landscape. Lots of energy is embedded in potable water due to pumping and purifying the water to make it clean and safe for human consumption.

California is Suffering a Water Shortage

California’s climate is a Medditeranean climate. Winters are mild with some rain while summers are hot and dry. Because most plants, especially exotic species, grow during the warm, dry time of the year when rainfall is mostly nonexistent. As a result, residents use between 30 and 50 percent of their potable water to irrigate landscape plants.

Periodic droughts also contribute to a limited water supply. Although the last drought is officially over, periodic water shortages caused by weather are naturally recurring events in the state.

Landscape architects and their clients are affected by periodic water shortages. During the worst part of the last drought, some cities implemented restrictions on outdoor water use. Homeowners in Los Angeles were fined by an army of code enforcement officers who roamed the streets looking for clandestine gardeners who flagrantly violated the city’s water restrictions. The severity of the drought and local jurisdictions’ reaction to the state’s shrinking water supply have created a political climate where water conservation and efficient irrigation system design is a non-negotiable part of the design process.

Preserving potable water is critical to the survival of Californians and landscape architects can really improve how up to half of the potable water supply is used by designing efficient irrigation systems and using alternative water sources.

Next: Recycled water in the landscape


John is a landscape architect who is currently preparing to take the California Supplemental Exam to become licensed in California. He is currently a licensed professional landscape architect in Georgia and Florida. John graduated from California State University, Pomona with a BSLA degree in landscape architecture in 1997 and has extensive practice experience in residential and commercial landscape design.

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