L-5480 9-08 Onsite wastewater treatment systems Graywater tank Blackwater tank Figure 1: A home with separate blackwater and graywater plumbing systems. Graywater safety Rebecca Melton and Bruce Lesikar Extension Assistant and Professor and Extension Agricultural Engineer The Texas A&M System hen homeowners use graywater to water their lawns, they help preserve washed materials soiled with human limited water supplies, reduce the demand for potable water for lawn waste (such as diapers) and water that Wirrigation and decr,ease the amount of wastewater entering sewers or has been in contact with toilet waste. onsite wastewater treatment systems. A graywater system may collect water from a single approved source However, homeowners who What is in graywater? or from any combination of those irrigate their lawns with graywater sources. The amount and quality The Texas Administrative Code need to understand the risks and of the graywater depends on the defines graywater as water from these safety issues associated with such use. sources. residential sources: Residential wastewater can be They should know the constituents ✔ of graywater as well as their potential Showers and bathtubs classified as either blackwater (sew- ✔ effects on human, soil, plant, and Sinks, except those used for age containing fecal matter or food environmental health. disposal of hazardous or toxic wastes) or graywater. If graywater is materials or for food preparation collected separately from blackwater, or disposal it can be dispersed as irrigation water ✔ Clothes-washing machines with less treatment than is required The code excludes water that has for blackwater. Table 1 includes a partial list of Table 1. Wastewater constituents from various residential sources. constituents that may be present in Shower Sinks Laundry graywater, illustrating that if some- and bathtub (not kitchen) thing is washed down the drain, it Bacteria • • will end up in the graywater. Several factors affect the com- Bleach • position of graywater, including the Grease and oil • • • quality of the water supply; the resi- dents’ personal habits; soaps, deter- Hair • gents, and cleaners used in the home; High pH • the age and number of residents in the home; the graywater treatment Hot water • • • process (if any); and the length of Nitrogen • graywater storage time. For example, a study in 2001 by Odor • • the University of Arizona found that Organic matter (BOD)† • • a home with two adults and a child had a significantly higher concentra- Phosphorus • tion of fecal coliform (microorgan- Salinity • isms found in human waste) in the graywater than did a household of Soap • • • just two adults. Sodium • Graywater will have higher concentrations of chemicals from Suspended solids • • • detergents and cleaners if strong Turbidity • • • products are used in the home and †Biochemical oxygen demand, a measure of organic contamination if the products are used often. Also, any treatment of the graywater and Often graywater has already ✔ Avoid irrigating edible fruit and the length of time it is stored before come into contact with humans—at vegetable gardens with graywa- application will influence its levels of sinks and in showers and tubs— ter. suspended solids, nutrients, bacteria, before it enters the graywater system. ✔ Discourage children from play- viruses, and odor. There is some concern that bacteria ing in areas where graywater is When homeowners use gray- can accumulate and grow in the regularly applied. water for landscape irrigation, they graywater storage system and that ✔ Never use graywater to wash should understand that the water graywater can be exposed to people down driveways, patios, or other contains constituents that may influ- who do not live in the house where it impervious surfaces. ence whether it is appropriate for use. originated. In addition to using graywater in As shown by several research stud- To eliminate possible exposure, areas that reduce the risk to human ies, the amount of contaminants in homeowners should choose the health, homeowners should make graywater varies greatly (Table 2). The distribution method and application sure that the system is designed and quality of graywater is lower than that areas carefully. For example, never operated to prevent inadvertent expo- of drinking water but higher than use spray distribution (sprinklers) sure to people: that of raw municipal wastewater. to apply graywater because it is the ✔ Prevent cross-contamination by method most likely to cause human using backflow prevention valves. Preventing harm exposure. The method least likely to ✔ Direct the overflow from the to people cause human exposure is a subsurface graywater reservoir to an onsite distribution system. The risk that graywater may pose wastewater treatment system or to human health is not as great as is If graywater is applied to the municipal sewer. often assumed. Although many of the soil surface (in a method other than ✔ Color-code all graywater com- contaminants in graywater may harm spray), take these steps to prevent ponents with purple markings your health (Table 3), the damage oc- exposure to people: to identify the water in them as curs only if the graywater is ingested ✔ Apply the graywater to areas that unsuitable for drinking. or otherwise contacted physically. receive little or no traffic. ✔ Wear latex or surgical gloves when handling components of Table 2. Concentrations of contaminants in graywater and raw wastewater and the maximum allowable concentrations in drinking water. Graywater studies Constituent Units Standard Water Drinking Protection (Environmental Agency, 2006) Typical Raw Wastewater (University of Arizona, 2001) Michigan, of University 1974 Urban Water Research Association of Australia (includes kitchen waste) University of Arizona, 2001 University of Arizona, 1991 New Mexico, 1998 Journal of Environmental Health, 1978 University of Arizona, 1995 Barium mg/L 2 <1 41 BOD† mg/L 300 328 159 65 260 149 120 Cadmium mg/L 0.005 0.1 30– Chloride mg/L 250* 25 21 9.0 100 Copper mg/L 1.3 (1*) 0.11 130 CFU/100 107– 8.03 1.4 7.6± 0.8 Fecal coliform mL 10 7 6 10 X10 X10 Log10 Iron mg/L 0.3* 0.11 700 Lead mg/L 0.015 0.04 Manganese mg/L 0.05* <0.05 31 Nitrate/nitrite mg/L 10/1 0.9 0.3 9.3 0.12 1.8 pH mg/L 6.5–8.5* 7.2 7.3 7.5 6.5 6.8 6.7 Phosphorus mg/L 59 8.1 9.3 26 Sodium mg/L 80 73 Sulfate mg/L 250* 117 35 60 23 Suspended solids mg/L 192 33 160 162 40.3 Turbidity mg/L 5 49 100 43 76 Zinc mg/L 5* 0.62 100 *Indicates EPA secondary water quality standard, which means that removal of these constituents is not required. If the concentration exceeds this standard, the effect to the water will only be aesthetic (odor, color, bad taste, corrosion etc). † Biochemical oxygen demand, a measure of organic contamination the system to perform mainte- Generally, most of the graywater harm depends on the quality of the nance activities, such as cleaning and the nutrients in it will be used by graywater, the type of soil, and the filters. plants, and the dynamics of the soil geology of the site. should break down the other contam- Groundwater may become Avoiding harm inants. If the system is maintained contaminated if it contains large to the environment properly, the graywater should have amounts of industrial chemicals that little if any effect on groundwater (the The greatest environmental effect are not broken down by biological water beneath the ground surface, of using graywater is that it decreases and/or environmental processes. It such as in an aquifer) or surface water the demand for fresh water, preserv- can also become contaminated if the (water in rivers, lakes, and streams). ing limited water supplies. The use of graywater is applied to ponded soils graywater also reduces the amount of However, graywater can pollute or saturated soils. wastewater entering sewers or onsite groundwater and surface water if it is Surface water may be affected if wastewater treatment systems. not applied properly. The amount of the graywater is applied to the ground Table 3. Potential health effects of contaminants. Contaminant Effect Barium Increase in blood pressure Cadmium Kidney damage Copper Short-term exposure: gastrointestinal distress Long-term exposure: liver or kidney damage Fecal coliform Short-term effects: diarrhea, cramps, nausea, headaches or other symptoms. Fecal coliform does not cause these symptoms, but its presence indicates that the water may be contaminated with micro- organisms that do cause the symptoms. Lead Infants and children: delays in physical or mental development Adults: kidney problems; high blood pressure Nitrate Infants below the age of 6 months who drink water containing nitrate above the drinking water standard could become seriously ill. Turbidity Although turbidity has no health effects, it can interfere with disinfection and provide a medium for microbial growth. Turbidity mayindicate the presence of disease-causing organisms, including bacteria, viruses and parasites that can cause symptoms such as nausea, cramps, diarrhea and associated headaches. Source: Adapted from U.S. Environmental Protection Agency, 2006 surface and it runs off into streams Sodium not only increases the limiting the amount of harmful or lakes. To limit the risk to surface alkalinity of a soil, but it also can elements entering the graywater water resources, choose a site where greatly damage the soil structure and, streams, such as by selecting a the soil can absorb the graywater and over time, inhibit the soil’s ability to laundry detergent low in sodium. does not allow ponding. Apply the accept water. To counteract the effects graywater at a low rate and distribute of sodium and help restore the soil Reducing effects it uniformly. You may need to move structure and water absorption rates, on plants the drag hose to limit ponding and periodically add organic matter such A study in 2004 by North distribute the contaminants.