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This article was originally published in the July/August 1995 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.

 

 

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Home Energy Magazine Online July/August 1995

 

Graywater
An Option For
Household Water Reuse

by Dick Bennett

With household wastewater eligible for reuse in the landscape accounting for about half of all indoor water use, graywater systems make sense as a way to maintain landscapes and reduce water bills.

 

The use of graywater--recycled household water from showers, sinks, and clotheswashers--increased in California during the mid 1970s and again in the late 1980s and early 1990s. The reasons? Some homeowners sought ways to save their valued landscapes in response to bans on outside watering caused by severe water shortages. Others sought ways to reduce their water use in response to skyrocketing drought-related water rates. Others were motivated by concern for the environment. Graywater use was approved, as a temporary drought measure, in both Marin and Santa Barbara Counties in California in 1978. The State of California even provided tax relief to individuals who installed graywater systems. A particular hotbed of graywater activity was found in several areas of Santa Barbara County. City of Santa Barbara officials, in response to a severe water shortage in 1990, requested a 45% cutback in residential water use and also a ban on outside watering. It was estimated that in the nearby city of Goleta 5,000 of 11,000 residents had some form of graywater system in 1989.

Graywater is generally defined as untreated used household water from showers, bathtubs, bathroom washbasins, and clotheswashers. Graywater from these household sources can be used in the landscape, provided that it meets certain conditions.

Wastewater from toilets and from soiled diapers is not approved because it may contain disease-carrying viruses or bacteria. Wastewater from kitchen sinks and dishwashers is not approved because it poses problems associated with grease, food particles, and detergent. Wastewater from water softeners is not recommended because it contains high concentrations of salt.

A graywater system in the 1970s was often no more than a garden hose going from the bathtub or washing machine out to the garden. Graywater systems gradually got more sophisticated in the late 1980s, as guidelines for the safe use of graywater were developed, largely in response to concerns on the part of public health officials. Graywater guidelines quickly led to the formulation and adoption of graywater standards in the early 1990s, which became part of both the Uniform Plumbing Code and the California Plumbing Code. Figure 1 shows a schematic of a graywater system. Today, 15 to 20 companies in California offer graywater systems ranging from do-it-yourself models to models that are fully automated and self-cleaning. While most graywater systems are found in California, they are appropriate wherever supplemental irrigation is normally required.

Figure 1
Figure 1. Schematic of a residential graywater system


Untapped Potential

Although most homeowners who began using graywater did so to save their landscapes and reduce their water bills, many have discovered additional benefits. These include recovery of nutrients, reduced use of fertilizer, a healthier landscape, reduced septic tank flows, and various community benefits.

Household wastewater eligible for reuse in the landscape accounts for about 50% of indoor water use. For the average family of four this translates into a potential daily water savings of around 140 gallons or about 35 gallons per person per day. The actual annual water savings for each household depends upon indoor water use patterns, type of water using fixtures and appliances, the irrigated area, plant types, and the climate of the region.

A graywater system can be like a landscape insurance policy. If a water agency bans landscape irrigation during a severe water shortage, the graywater-irrigated landscape will survive. This can represent a significant cost avoidance to a homeowner, since the value of a landscape can often be 5%-10% of the value of a home. Using graywater also saves energy because when water travels from its source to house to sewage plant, energy is used to pump and treat it.

Using graywater improves the efficiency of applied water because it is delivered to the plants underground--eliminating runoff, overspray, and evaporation.

Valuable plant nutrients, such as phosphorous and potassium, are often found in graywater. Graywater use can result in healthier plants and in the reduced application of fertilizers. And, by leaving the soil surface drier, it may also make for a healthier landscape by reducing disease and pests.

Homeowners sometimes remove graywater streams from their household waste streams to reduce the flow to their septic tanks. This provides for longer treatment times and reduces the hydraulic loading on their leach lines.

The community benefits from graywater use because it reduces the amount of wastewater that is discharged to the local treatment facility. This has the potential to reduce wastewater treatment costs and may even postpone or avoid the need for flow-related expansions of the facility. Local water and wastewater agencies also experience reduced pumping costs.

Graywater Systems

A graywater system has three distinct elements: the drain-line plumbing, the surge tank and associated components, and the irrigation delivery system. Figure 2 (taken from Appendix J of the California Plumbing Code) identifies the various components of a graywater system where no pumping is required to deliver the graywater to the landscape.

Some plumbing work is required, however, because the graywater must be diverted from some of the existing drain lines. The various graywater source drain lines must then be connected to a common line to the surge tank which contains the valves, pumps, vents, controllers, and filters. Several types of these various components are available depending upon the level of sophistication desired. For example, the filter can range from a nylon stocking to a mesh screen to a sand filter.

Pumps are needed to deliver the graywater to the landscape if drip irrigation (rather than a leach field) is used or if the landscape is above the level of the surge tank. The size of the pump is determined by several factors. These are the height to which the graywater must be pumped (called head), the distance from the tank to the landscape, and the pressure required by the system to deliver the required discharge rate. For level lots, a 1/2-horsepower centripetal pump is usually adequate. For a family of four, the pump would run for about five minutes a day during the irrigation season and would draw 2 to 4 amps of power while running. While the homeowner would incur a slight increase in energy costs, the total energy use in the community would remain about constant since the water and wastewater systems would realize an energy savings due to reduced pumping costs.

One of the toughest challenges in designing the graywater system is laying out the irrigation system and determining the size of the area to be irrigated. The homeowner or designer must decide which plants can be irrigated with graywater. The irrigated area is determined by the type of soil, by the volume of graywater produced, and by the summer water requirements of the plants. Table 1 presents a hypothetical example for determining the water requirements of different plants.

Figure 2
Figure 2. Schematic of a single-tanked, pumped, residential graywater system.

Table 1. Plant Water Needs

       
Climate Relative Water Need of Plant

Gallons Per Week

   
  Plant Factor

200 ft2

100 ft2

50 ft2

Coastal
(ET*=1 in/wk)
low water using (0.3)
medium water using (0.5)
high water using (0.8)

38
62
100

19
31
50

10
16
25

Inland
(ET=2 in/wk)
low water using (0.3)
medium water using (0.5)
high water using

76
124
200

38
62
100

19
31
50

Desert
(ET=3 in/wk)
low water using (0.3)
medium water using (0.5)
high water using (0.8)

114
186
300

57
93
150

28
47
75

*ET stands for evapotranspiration.

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.)

Example: The 1,120 gallons of graywater per week produced by the Brown family could irrigate:

       
8 young fruit trees
8 medium-sized shade trees
7 large shrubs
8 x 50 = 400 gallons
8 x 62 = 496
7 x 31 = 217
(high water using, 50 foot canopy)
(med. water using, 100 foot canopy)
(med.water using, 50 foot canopy)
   
total:

1,113 gallons per week

     

System Costs

Installation costs for graywater systems can range from several hundred dollars to more than $5,000. Table 2 compares the costs of installing various graywater systems. Note, however, that a fully automated, do-it-yourself system (except for the drain line plumbing and the irrigation system) recently became available for under $1,000. Table 3 itemizes the cost (based on 1994 figures) for each component of the graywater system.

Costs also depend on whether the system is going into an existing or new dwelling and whether the dwelling has a raised or slab foundation. Costs are usually lowest for new construction and highest for existing dwellings with slab foundations. In fact, it is so expensive to install a complete graywater system in an existing home with a slab foundation that only effluent from the washing machine should be considered in this situation.

Table 2. Types of Systems Currently Available

     
System Type Source of Graywater Features Cost
Low -tech
owner or
professional
installation
Washing machine only 200 micron mesh filter
55 gal garbage can w/locking lid

$400

$800

Medium-tech Uses all graywater sources Sump pump to pvc tubing
Subsurface drip irrigation
200-micron mesh filter
(2) 55 gal. storage tanks

$1,000
$1,500

Fully automated

Professional
installation

Uses all graywater sources Automatically back-washed sand filter
250 gallon storage tanks
Pumps at both source and tank/filter
3-way valve, backflow preventers
Microprocessor controls all flows
Backed by potable water

$2,500
$5,000

Table 3. Parts and Approximate Costs

 
Parts

Approximate
Cost ($)

Washing machine hook-up
connection parts
three-way diverter valve
pipe to sewer
pipe to tank
sanitary tee


20
28
4
4
3
 

Shower/bath hook-up
connection parts
pipe to tank
bends
fittings
vent

15
4
15
15
13
Total: Plumbing Parts

121

55 gallon tank with lid
vent
inlet pipe
overflow pipe
drain pipe
backwater valve
water seal type trap
emergency drain ball valve
tank adapters($20 each, one for each pipe)
union
101
13
4
4
4
4
3
28
60
12
Total: Tank Parts
Total: Pump
233
150
And  
Subsurface Drip Irrigation System
filter 140 mesh one-inch 25 gal/min
pipe: PVC class 200 (100 ft)
fittings: schedule 40
drip lines 336 emitters
automatic flush valve ($2 each)
controller
switches
control valves ($25 each)
pressure reducing valve
compression T's

25
30
45
138
4
50
32
50
15
4
Total: Drip Parts 393
Or  
Mini-leachfield
solid pipe
perforated pipe: 180ft.
gravel, 18 in/130/1 = 7 yards
landscape filter fabric


50
70
70
40

Total: Leachfield Parts

Grand Total: Drip
Grand Total: Leachfield

230

897
734


* Cost for permit fees, rental equipment, professional
installation, and maintenance not included.

Health and Water Quality

Two areas of concern regarding graywater use involve health and water quality. Since graywater can contain infectious organisms, safety standards were needed before health officials would sanction its use.

In 1991, the City of Los Angeles conducted a one-year study of graywater use at eight residential test sites to make recommendations for, among other things, the safe use of graywater. Bacteria in the soil were found at both graywater and nongraywater irrigated areas in the test landscapes. While bacteria increased in the soil where graywater was used, disease organisms were not found at any of the test sites. One conclusion was that graywater ... does not pose a significant risk to users or the community. Another finding of this study was that soils contain a lot of animal fecal matter. The results led one observer to conclude, Don't eat dirt. Note that although graywater has been used in California for about 20 years without permits, there has not been one documented case of disease transmission.

In 1992, Appendix G (originally Appendix W) was added to the Uniform Plumbing Code of the International Association of Plumbing and Mechanical Officials (IAPMO). This appendix established standards for the use of graywater in 22 Western states. In November, 1994, Appendix J of the California Plumbing Code went into effect, permitting the use of graywater in single-family residences for subsurface landscape irrigation. To date, California is the only state to adopt Appendix G, in a slightly modified form.

There are several important rules regarding the safe use of graywater. In California, graywater use is permitted only at single-family dwellings. The California Plumbing Code requires that graywater be delivered to the landscape through a mini-leach field (at least 17 in below the surface) or a subsurface drip irrigation system (at least 9 in below the surface) to avoid runoff, surface pooling, and spray (see Figure 3). The Uniform Plumbing Code does not permit the use of drip irrigation, only mini-leach fields, which must be 18 in below the surface. Graywater use is not permitted where soil conditions do not allow for adequate drainage or where groundwater could be contaminated (within 5 ft of the surface).

Some observers believe the codes could be improved if the subsurface application were allowed to occur within several inches of the soil surface to better irrigate those plants with shallow root systems and to take advantage of the higher concentration of bacteria in the soil. (Ninety percent of the bacteria in the soil occurs within the top 18 in.) Bacteria are responsible for the rapid breakdown of graywater constituents into water-soluble plant nutrients.

Cleansers to Avoid

While most detergents can be used with graywater systems, there are several important exceptions and several cautions. Products that contain boron, such as Boraxo and Borateam, should not be used. Boron has been shown to be very toxic to most plants. If salt buildup in the landscape is a concern (it should be, in most cases) it is better to use liquid detergents than powdered detergents. Powdered detergents contain excessive amounts of sodium, which is often used as a filler. Since detergents are alkaline, acid-loving plants (generally those which like shade, but check with the local nursery) should not be considered for graywater application. Homeowners with graywater systems generally need to be conscious of what they put into the graywater drain lines, from the type of laundry detergent to household cleaners.


Chlorine is extremely toxic to plants, but it has not generally been a problem in graywater irrigation, according to one reputable source. This may be because chlorine breaks down fairly rapidly and its effects may also be dissipated or diluted in the soil. Having some residual chlorine present in the surge tank to minimize bacteria buildup also appears to be a benefit.

Finally, graywater should not come in contact with the edible portion of fruits and vegetables (for instance, with root vegetables, such as carrots, radishes, potatoes, and beets).

Figure 3
Figure 3. Conceptual schematic of a potential irrigation layout for a graywater system.

Water Rates: An Affordable Housing Issue?

Water rates are increasing dramatically. During the 1980s, water rates rose at an average annual rate of 7%, or about twice the rate of inflation. This trend has continued during the first half of the 1990s, and the end is not in sight. Water rates are climbing because of additional water quality regulations, the need to replace an aging infrastructure, and general cost increases, among other factors.

As water rates continue to rise, low-income families will be particularly hard hit. Dozens of water utilities have already developed special payment programs for poor or elderly customers. Over the next few years, however, water utilities will increasingly recognize that effective conservation programs targeting low-income families can

  • Reduce low-income customers' water bills.
  • Reduce system-wide demand.
  • Reduce the utility's exposure to unpaid water bills.
  • Reduce the utility's collection expenses.

The overall level of water rates in large cities tends to be fairly low (around $150 per year, as of 1992). When compared to the nationwide median household income (about $31,000 in 1993), water rates average less than 0.5% of income.

Just looking at these averages would lead one to conclude that water rates should remain affordable for quite some time. Yet more and more people--ranging from lenders to state public utility commissioners to utility executives and board members--are concerned about the ability of low-income people to afford water service.

These concerns are real, but they cannot be measured by looking at broad averages. Providing affordable water service is a matter of protecting low-income families, not the average family. When water rates are compared to the incomes of poorer families, a very different picture emerges, and the increasing concern with affordable water service begins to make sense. A critical factor is that the incomes of low-income families do not keep pace with inflation. For example, in 11 states the maximum welfare payment to families with children did not change at all between 1988 and 1991, even though inflation averaged 4% to 5% per year.

Nationally, of the 80 million households that receive publicly-supplied water, 14 million had annual incomes below $10,000 in 1989. Another 15 million water customers had annual incomes between $10,000 and $20,000. In all, more than one-third of water customers had annual household incomes below $20,000.

At these income levels, the family must cut back on expenses. Typically, these expenses include health care, food, and household repairs, among others. Buying efficient plumbing fixtures or fixing small water leaks is very low on the priority list.

I recently conducted a study of water rates and incomes in Pennsylvania. The study found that water rates are least affordable for low-income families in cities of more than 100,000 population, even though these cities had some of the lowest water rates in the state. By comparing the typical water bill to income distribution curves, I determined that 25% of the water customers in large cities are paying at least 2% of their income for water, and 10% are paying more than 4% of their income for water (this does not include the cost of sewer service).

Many low-income families live in subsidized housing that includes water charges in the rent, but this does not eliminate the need for conservation programs aimed at low-income families. As water bills continue to climb, owners of rental properties and the providers of rent subsidies will probably either raise the renters' contribution or require renters to pay their water bills directly. Large water utilities, thus, should be examining water conservation programs that target low-income families. Such programs can be highly beneficial to the customers and the water utility as a whole.

As an example, Philadelphia's recent pilot water conservation program, targeted to customers with incomes under 150% of the poverty level, was highly successful. The program involved installing toilet dams, low-flow showerheads, and faucet aerators, in addition to fixing leaks. Customers were also educated about ways they could conserve water. An evaluation of Philadephia's program found that 390 households reduced their water consumption by an average of more than 25%, saving an average of $50 per household per year for water and sewer service (compared to the program cost of $90 per household). The resulting payback of less than two years (not including energy savings for reduced hot water consumption) made the program highly cost-effective. Philadelphia is broadening the implementation of this program because it reduces the bills of poor families and also lessens the city's exposure to unpaid accounts.

In summary, water rates will continue to increase much faster than the incomes of low-income people. Large water utilities will face a growing problem of uncollectible bills, and poor families will run the risk of losing their water service. Water conservation programs targeted to poor families can help eliminate these problems and ensure that poor families do not lose water service. Increased water costs may also present an opportunity for water and energy utilities, as well as other organizations, to cooperate in combined efficiency projects, thereby extending the reach and effectiveness of their programs (see Pulling Utilities Together: Water-Energy Partnerships, HE July/Aug '93, p. 17).

Additional Reading

Beecher, J.A. Water Affordability and Alternatives to Service Disconnection. Journal of the American Water Works Association (AWWA) 86 (October 1994) 61.

Duke, E.M. and A.C. Montoya.Trends in Water Pricing: Results of Ernst & Young's National Rate Surveys. Journal AWWA 85 (May 1993) 55.

National Consumer Law Center, Energy and the Poor: The Crisis Continues. Chapter 2 (1995).

Rubin, S.J. Are Water Rates Becoming Unaffordable? Journal AWWA 86 (February 1994) 79.

Russell, D.F. and C.P.N. Woodcock What Will Water Rates be Like in the 1990s? Journal AWWA 84 (September 1992)68.

--Scott J. Rubin

Scott J. Rubin, an attorney and consultant in Selinsgrove, Pennsylvania, specializes in issues affecting the water and electric utility industries.

 

Graywater's Future

Even in some areas affected by severe water shortages, graywater use is still quite low. A survey conducted in the East San Francisco Bay area in 1994 indicated that only 2% of single-family households had graywater systems and that about 25% of the people surveyed had never heard of the term graywater.

Bay Area water agencies requested up to a 25% cutback in water use during the 1987-1992 drought period. In areas where water agencies requested higher cutbacks and/or issued bans on outside watering, a higher percentage of graywater systems are found. Studies planned over the next few years will seek to determine

How people feel about their graywater systems.

  • Water savings from graywater systems.
  • The long-term effect on the landscape.
  • Maintenance requirements.
  • Operating costs.

Answers to these questions will shed more light on the real benefits and costs of using graywater.

Legislation recently introduced in California (Assembly Bill 313) would allow for the safe use of graywater at sites besides single-family residences. In the future, new single-family homes may even be required to be plumbed to allow for graywater use. Graywater use is expected to increase slowly as more people become aware of its benefits and as the costs of ensuring a reliable water supply increase.

Further Reading

Using Graywater in Your Home Landscape: Graywater Guide, California Department of Water Resources. P.O. Box 942836, Sacramento, CA 94236-0001.

Create an Oasis with Greywater: Your Complete Guide to Managing Greywater in the Landscape ($9) and Building Professionals Supplement: Your Complete Guide to Professional Installation of Graywater Systems ($13). Both available from Oasis Biocompatible Products, 5 San Marcos Trout Club, Santa Barbara, CA 93105-9726.

Dick Bennett is Water Conservation Administrator at the East Bay Municipal Utility District in Oakland, California.

 

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