3.5: Outdoor Water Use

How much water is used outdoors? Most estimates for outdoor water use in the United States suggest that it is more than 50% of all water used for residential use. In general, the hotter the locale, the more water is used for landscaping.

Learning Objectives

In this section, you will:

• Identify the benefits and needs of landscape
• Differentiate among types of irrigation
• Classify plants according to their watering needs
• Design a landscape with best practices in mind

Why don’t we get rid of all the landscape, cover the ground with cement, and save all that water? Landscape serves a variety of purposes, and is considered a beneficial use of water. After all, plants make oxygen, and we humans love oxygen. Plants also lower the air temperature. An entirely paved landscape would be a hot one - check out the center of a parking lot in the summer. And soil acts as a giant sponge, absorbing and filtering water, which eventually allows for aquifers to replenish. So, keeping landscape is a given, and acknowledging that live plants in the landscapes need water is important. However, choosing a waterwise landscape and giving it just the water it needs is essential.

Couldn’t all of our irrigation problems be solved if we saved the rainwater that falls from the sky? Doesn't that just go to waste if it runs into the ocean? We do save it in both surface reservoirs and in groundwater aquifers. Water isn’t wasted if it infiltrates. And even when it runs into the ocean, it is still part of the water cycle.

Sometimes, rain barrels are presented as the perfect solution to irrigating landscape. However, rain barrels bring with them a host (no pun intended) of other problems, including providing the perfect breeding ground for mosquitoes. We are poised on having a worldwide explosion of babies with microcephaly, caused by the Zika virus, which is spread by mosquitoes.

Figure \(\PageIndex{1}\)

Additionally, mosquitoes spread the West Nile Virus, and a number of locations in Southern California, including Santa Clarita, are “hot spots” for the disease. It is almost impossible to mosquito-proof a rain barrel—mosquitoes will enter that smallest opening to lay eggs in water. This makes rain barrels perfect for breeding mosquitoes, and not for saving water.

Figure \(\PageIndex{2}\): West Nile Virus Activity map by the California Department of Public Health is in the public domain

Setting mosquitoes aside, why wouldn’t rain barrels help save water? In Southern California, most of the rainfall occurs when the plant water needs are the least. Rain barrels may be a good solution in places like Arizona and New Mexico, which get summer monsoonal storms when the water needs for plants are the greatest. In California, our storm season generally lasts from November through February when the plant water needs are the least.

Best Practices in Landscapes

It is a much better idea to look beyond rain barrels and beyond eliminating landscape entirely to principles that would help landscape use water more efficiently. These are practices that are a compromise between what is called “all or nothing” thinking. You will hear a lot of this sort of thinking as you hear people talk about their landscape. This is the sort of thinking that says, “If I can’t have my grass in the front and backyard, then I’m going to pave over everything” or “If I can only water twice a week, I’m just going to give up and let everything die.” In the next part, you will learn a few of the principles that landscape professionals use to create and maintain drought-tolerant landscapes. There is a middle ground between paving everything and having no landscape and having turf grass everywhere.

Maintain the irrigation system—This means conducting a regular review of the system while it is running to look for common problems (overspray, clogged nozzles, blocked heads). Much like we learned in the section on alternative water supplies, including gray water, frequently maintenance is a hurdle that homeowners do not want to overcome. If something needs maintenance, such as a gray water system or an irrigation system, it may simply be avoided and neglected. There is water-saving potential in conducting maintenance.

Mulch the exposed soil—Any surface that is not covered by a plant (or a six inch space around a plant) should be covered with three to five inches of mulch. Mulch has a ton of benefits including keeping the soil temperature more moderate (warmer in the winter and cooler in the summer), preventing weeds from sprouting in soil and decreasing the evaporation. Mulch does need to be raked periodically and re-applied year to year, but it makes a great improvement in the aesthetics and health of a planted surface.

Hydrozone—The highest water use plants used in California landscapes are types of turf, including cool season turf, which has slender blades of darker green color, and warm season turf, which has wider blades of medium-green color. You can see in the table below how the water needs, measured in evapotranspiration in inches per day, vary tremendously among types of turf grasses. Typically, when someone admires a lawn, the lawn is Kentucky blue grass or another cool season turf grass. There are low water using options, such as Buffalo grass, which can easily use half as much water. But grass overall is still a very water thirsty plant.

Relative Ranking	ET in inches/day	Cool Season	Warm Season
Very low	< 0.24		Buffalo grass
Low	0.24-0.28		Bermuda grass Zoysia grass
Medium	0.28-0.33	Red fescue St. Augustine
High	0.33-0.39	Perrential Rye grass Kikuyu grass
Very high	> 0.39	Annual bluegrass Kentucky blue grass Annual rye grass

Hydrozoning, or separating your plants by their water needs, helps you water the right amount in each zone. In the table below, you can see how you might group plants according to their high, moderate, low and very low water needs. Each plant is compared to a cool season turf grass of 4-7 inches tall that is not stressed. This is the plant with the highest water need. Trees and shrubs should be in their own zone. Anything drought-tolerant typically has a low water need and should be in a separate zone. And anything with a very low water need typically does not need irrigation. Note that a plant with moderate water needs only needs 40-60% of the water of a cool season turf grass. That means that typically anything other than turf grass will need half as much water - this is truly astounding.

Water Needs	Percent of Reference ET	Types of Plants
High	70-90% ET	Most turf grasses
Moderate	40-60% ET	Most trees and shrubs
Low	10-30% ET	Drought-tolerant plants, like salvia (sages)
Very Low	<10% ET	Cacti

Irrigate deeply and water infrequently—Daily watering isn’t necessary for most plants, including turf grass, even during the summer. Irrigation depends on a number of factors, including:

Soil type—Both clay and sandy soil in your yard mean you must irrigate in short bursts and allow water to sink in in between bursts. This is typically called cycle and soak because you allow the controller to cycle on once and then let the water soak in before cycling on again.

Depth of roots—If you water grass multiple times a day, you train the grass to have short roots, which mean the roots cannot reach other available water deeper in the soil. Try to water less frequently to encourage deeper roots to grow.

Seasonal variation—Plants have greater water needs in the summer than the spring, fall or winter. This is intuitive, but many people water the same amount of time all year round.

Types of plant material—Would you water your lawn and a cactus the same amount? Of course not. But many people water everything in their yard the same amount, which usually results in over-irrigation of most non-grass plants. This is why separating your yard into hydrozones is so important.

Irrigation system type—Spray heads put out water much faster than rotating heads or than drip irrigation - you need to understand this when you program your system. Spray heads and rotating heads can be high-efficiency, meaning they apply water at a slower rate. Spray and rotating nozzles are appropriate for grass, but drip irrigation is a more appropriate choice for shrubs and trees. The table below summarizes the four major types of irrigation, including their water pattern, ideal use, and precipitation (precip) rate, which is the amount of water that the irrigation type puts out.

Irrigation Type	Water Pattern	Ideal for...	Precipitation Rate	How to irrigate well with it?
Spray	fan	turf grass	Faster than soil can absorb	Cycle and soak
Rotating	stream	turf grass	Faster than soil can absorb	Cycle and soak
Bubbler	gush	trees with wells	Faster than soil can absorb	One run time to fill the wells
Drip	drip	shrubs and trees	Same rate soil can absorb	One long run time (45 minutes +)

Irrigation Controllers

In California, any new homes will come with a weather-based or soil-moisture-based irrigation controller. This means that some of the guess work will be taken out of irrigation decisions. Typically people have no idea how much to water and end up over-irrigating everything. Irrigation controllers can be programmed by the days to water, the time of days to water (called the start time), the length of time to water (called the run time). A weather-based irrigation controller or a soil-moisture based irrigation controller needs to be guided on what days to water and what times to start, but can determine how long to water based on weather or on soil moisture.

When do you think you might see savings from using a weather-based irrigation controller? Typically, people set their controller at the summer levels for irrigation and keep the controller at that level all year. This means they are watering both more frequently than needed and longer than needed for most of the year. The savings when upgrading to a weather-based irrigation controller come in the spring, fall and winter, when the person was over-irrigating.

Grass and Artificial Turf

When is grass appropriate? Are people playing on the surface? If so, grass is the perfect plant - no other plant will take being trampled and literally bounce back. If kids or adults are using the grass to play on, keep it. It’s the right plant in the right place at the right time. But the way grass is used in many communities is as a default plant. Grass is easy and inexpensive to install and has been installed in all sorts of places that are hard to irrigate without run-off, like parkways, hills and slopes or medians.

What about artificial turf? While artificial turf does not change the landscape aesthetic in a community, it has both benefits and drawbacks, which are detailed in the table below.

Benefits of Artificial Turf	Drawbacks of Artificial Turf
It’s green	It can become hot in the sun (and contribute to a heat island effect on your property)
It saves water	Many installers recommend hosing down artificial turf for dust control and to clean pet waste
No mowing is necessary	It can photodegrade in the sun (10-year lifespan)
No fertilizers are necessary	It will smell of pet waste if not cleaned effectively
Costs incurred are most likely one time charges (until time for replacement in around 10 years)	Typically, artificial turf is $10-15 a square foot

There are other types of outdoor water use, but they are negligible in the greater scheme of things when compared to landscaping. For example, leaks may occur outdoors in the irrigation system. Water can also be used for cleaning hardscape (pavement, sidewalks, driveways), washing vehicles, filling fountains and swimming pools.

Try It!

1. Propose a strategy for landscaping an area that you see frequently, such as your home, a local park, or your school. This could be your front or backyard, a common area, or an area at work. Consider the types of plants that you might install, an arrangement for them, the irrigation system you should use, and what obstacles you might encounter along the way. Identify the best practices you have used.
2. A friend wants to install artificial turf in his front and backyard. Give an overview of the benefits and drawbacks of artificial turf.

Key Terms

Cycle and soak—Irrigating in short bursts and allow water to sink in between bursts

Hydrozoning—Separating your plants by their water needs, which helps you water the right amount in each zone