«Graywater in Your Home Landscape Graywater Guide January 1995 David N. Kennedy Pete Wilson Douglas P. Wheeler Director Governor Secretary for ...»
Using Graywater in Your Home Landscape
David N. Kennedy
Pete Wilson Douglas P. Wheeler
Governor Secretary for Resources
Department of Water Resources
State of California The Resources Agency
Using Graywater in Your Home Landscape
OF WATER R
DEPARTRCES IA ST A N TE R
O F CAL IF OJanuary 1995 David N. Kennedy Pete Wilson Douglas P. Wheeler Director Governor Secretary for Resources Department of Water Resources State of California The Resources Agency Graywater is untreated household waste water which has not come into contact with toilet waste.
Includes: used water from bat
Thanks to the Urban Water Research Association of Australia for their contribution of four illustrations from their publication, Domestic Greywater Reuse: Overseas Practice and its Applicability to Australia.
Foreword California's Graywater Standards are now part of the State Plumbing Code, making it legal to use graywater everywhere in California. These standards were developed and adopted in response to Assembly Bill 3518, the Graywater Systems for Single Family Residences Act of 1992.
This Guide was prepared to help homeowners and landscape and plumbing contractors understand the Graywater Standards and to help them design, install and maintain graywater systems.
Carlos Madrid Chief, Division of Local Assistance Table Of Contents Foreword
I. Why Use Graywater?
II. The Seven Steps
1. Investigate the Permit Process
2. Prepare the Plan
Estimate the Amount of Graywater Your Family Will Produce
Estimate the Amount of Landscape You Can Irrigate
Gather Soil and Ground Water Data
Draw a Plot Plan
Determine the Size of the Irrigated Area
Determine the Location of the Graywater System
3. Design the Graywater System
Plumbing System: Pipes and Valves
Subsurface Drip Irrigation System
4. Submit the Plan for Review and Approval
5. Install the System
Purchase the Equipment
Install the Plumbing System
Install the Subsurface Drip Irrigation System
Install the Mini-Leachfield System
6. System Inspection and Approval
7. Using, Monitoring and Maintaining the System
Select Garden-Friendly Soaps
Keep Soils Healthy
Grow Healthy Plants
Monitor and Maintain the System
III. Appendix California Graywater Standards
Graywater Measures Checklist
Historical Evapotranspiration Values in Inches for July
This report was written by:
With the assistance of:
Write to: California Department of Water Resources, P.O. Box 942836, Sacramento, 94236-0001 or call Marsha Prillwitz at (916) 327-1620.
Why Use Graywater?
Are you tired of watching your bathing and laundry water go down the drain when it could be put to good use on your landscape? Now it is safe and legal to reuse that "graywater" and this guide shows you how.
In addition to conserving water and probably reducing your water and sewer bills, you will also be "drought-proofing" your landscape by using graywater. Since more than half of your indoor water can be reused as graywater, during shortages, when outdoor watering may be restricted, you will have a constant source of water. With landscapes valued at between 5 percent and 10 percent of the value of a home, this back-up supply of water may be an important economic insurance policy for you. Furthermore, the nutrients in graywater may be beneficial to your plants.
The seven steps to follow to put graywater to use in your landscape are:
If you decide not to do some of the steps yourself, you can hire a landscape contractor to install the irrigation system or a plumbing contractor to install the plumbing. They will follow this same process.
To better illustrate how to install a residential graywater system, this guide features the Brown family. In examples throughout the text, this family of four follows the seven steps.
The Seven Steps The following seven steps will help you plan, design, install, and maintain your graywater system.
1. Investigate the Permit Process Information in this guide is based on the California Graywater Standards. In the appendix, you will find a copy of Title 24, Part 5, of the California Administrative Code, GRAYWATER SYSTEMS FOR SINGLE FAMILY DWELLINGS, commonly called the California Graywater Standards (Appendix J). These are the official rules for using graywater in California.
The Standards require that a building permit be obtained before a graywater system is installed. Check with your local building department for information on their permit process and any variations made to the Graywater Standards before you proceed.
2. Prepare the Plan Is a graywater system for you? By first learning approximately how much graywater your family will produce and how much landscape you can irrigate with it, you will be better able to decide. Determining whether your soil is suitable for a graywater system is another primary consideration. Once you have decided that a graywater system is in your future, the next step is to draw a plan and design your system.
Example: The Brown family has a three bedroom house so the system must be designed for a minimum of four people. If all fixtures are connected, then each occupant is assumed to produce 40 gallons of graywater per day, resulting in a total of 160 gallons each day.
The reason graywater flow is based upon the number of bedrooms rather than the actual number of people is that the number of bedrooms will remain constant, while the number of people may vary over time.
Estimate the Amount of Landscape You Can Irrigate Graywater is distributed subsurface and will efficiently maintain lawns, fruit trees, flowers, shrubs and groundcovers. It can be used to irrigate all plants at your home except vegetable gardens.
You do not need to do the following calculation as part of the permit process, but it will help you determine just how much landscape your graywater will irrigate and how many plumbing fixtures you may want to hook up to the system. On page 6, you will find specific information about determining the minimum required irrigated area.
You can estimate either the square footage of the landscape or the number of plants which can be irrigated. Generally, estimating the square footage is more useful for lawn areas and subsurface drip irrigation systems while estimating the number of plants would be more useful for trees and shrubs irrigated by a mini-leachfield system.
Use this formula to estimate the square footage of the landscape to be irrigated:
LA = GW ET x PF x 0.62
LA = landscaped area (square feet) GW = estimated graywater produced (gallons per week) ET = evapotranspiration* (inches per week) PF = plant factor 0.62 = conversion factor (from inches of ET to gallons per week) *Evapotranspiration is the amount of water lost through evaporation (E) from the soil and transpiration (T) from the plant. (This formula does not account for irrigation efficiency. If your irrigation system does not distribute water evenly, extra water will need to be applied.)
[The gallons per week calculation for this chart was determined with the following formula:
Gallons per week = ET x plant factor x area x.62 (conversion factor.)(This formula does not account for irrigation efficiency. If your irrigation system does not distribute water evenly, extra water will need to be applied.)]
The number of gallons of water per week a plant needs will vary from season to season, plant to plant, and site to site, but this will give you a general idea about the number of plants you can successfully irrigate in July with your graywater.
Irrigation needs of the landscape may be greater than the total available graywater.
So, even if the system includes the shower, tub and clothes washer, some supplemental water would be necessary during the hot summer months. Contrarily, the amount of available graywater may be greater than the amount you can use on the landscape. In that case, you can reduce the number of plumbing fixtures connected to the graywater system.
Gather Soil and Ground Water Data Determine the soil types and ground water level on your property. The local building department will probably provide this information or allow you to use Table J-2 of the Graywater Standards. If this information is not available, consult with the local building department about the approved soil testing method. They may require that you hire a qualified professional to conduct a percolation test, or may allow you to do it. Usually you would be required to dig test holes in close proximity to any proposed irrigation area and conduct a percolation test. The U.C. Cooperative Extension Office, the county agricultural agent or a local geologist, soil scientist or college instructor will be able to assist with soil type identification and characteristics. The United States Department of Agriculture Soil Conservation Service publishes a Soil Survey of every county which may be helpful for this purpose.
Draw a Plot Plan A plot plan of your property should be drawn to scale and may be required to include dimensions, lot lines, direction and approximate slope of the surface. The location of retaining walls, drainage channels, water supply lines, wells, paved areas, and structures should be included. If you have a septic tank, show the location of your sewage disposal system and the required 100 percent expansion area. Provide information on the number of bedrooms and which plumbing fixtures will be connected to the proposed graywater system. Finally, indicate the landscape area that you plan to irrigate with graywater.
Determine the Size of the Irrigated Area Above, you learned how to estimate the amount of landscape you can irrigate based on the graywater produced and the water needs of the plants. Now you need to determine the minimum size of the irrigation field required, based on soil type. With either a subsurface drip or minileachfield system, at least two irrigation zones are required and each must irrigate enough area to distribute all the graywater produced daily without surfacing.
For sub-surface drip irrigation systems, Table J-3 of the Graywater Standards is used to determine the number of emitters required. The emitters must be at least 14 inches apart in any direction.
Example: The Brown family produces 160 gallons of graywater per day and irrigates plants in a sandy loam soil. Based on Table J-3, the minimum number of emitters per gallons per day of graywater production is.7 x 160 = 112 emitters. With at least 14 inches between each emitter, the total irrigation area for one zone would be 112 emitters x 14 inches / 12 inches (to get square feet) = 130 square feet. The Browns would need 130 x 2 = 260 square feet for the minimum of two irrigation zones required by the Graywater Standards to safely distribute their graywater without surfacing.
As we discovered earlier, the Browns could irrigate up to 1129 square feet of lawn with 160 gallons of graywater per day. Therefore, they can design their system to irrigate over four times the minimum irrigated area in this case and still maintain a healthy landscape.
If the mini-leachfield irrigation system is used, the required square footage is determined from Table J-2 of the Graywater Standards.
Example: The Brown family produces 160 gallons of graywater per day and is irrigating a sandy loam soil. Based on Table J-2, the minimum square feet of irrigation area for a mini-leach field system would be 40 square feet per 100 gallons, (160/100=1.6)1.6 x 40 = 64 square feet. The Browns would need two irrigation zones, each 64 square feet in size, a total size of 128 square feet.
The Browns want to install a 100-foot line with a trench that is 8 inches wide to irrigate the 8 fruit trees and 7 large shrubs along the perimeter of their yard. Then, they want to install an 80 foot line with a trench that is 1 foot wide to irrigate 8 mature shade trees. To calculate the area of the minileachfield irrigation field, the length of the line as well as the width of the trench must be considered.
Therefore, the total area of the irrigation field would be 66 square feet (100 ft. length x.66 ft. width) + 80 square feet (80 ft. length times 1 ft. width) = 146 square feet. Since 146 square feet is greater than the minimum required irrigated area for a mini-leachfield (128 square feet), and since each zone is greater than the required 64 square feet, the Browns meet the minimum irrigated area requirement.
Determine Location of the Graywater System Once you know the size of the irrigation field, based on the soil and plant needs, you can decide where to put it. Table J-1 in the Graywater Standards establishes distances that the surge tank and irrigation field have to be from various features, such as buildings, septic tanks, and the domestic water line. In addition, your system must be designed so that no irrigation point is within five vertical feet of the highest known seasonal ground water.
3. Design the Graywater System T h e n ext s tep is to deter m in e th e differ en t com pon en ts of you r gr aywater s ys tem an d pr epar e a des cr iption of th e s ys tem its elf. I n clu ded will be a deter m in ation of th e ir r igated ar ea an d details of th e gr aywater s ys tem. T h is con s tr u ction plan in clu des a des cr iption of th e com plete in s tallation in clu din g m eth ods an d m ater ials.
A gr aywater s ys tem u s u ally con s is ts of: