How Can You Jump on the Graywater Reuse Trend?

The idea of diverting some household flows away from the septic tank for irrigation is appealing to homeowners and environmentalists. What do you need to know?

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We have conducted numerous basic workshops on soil treatment systems for industry professionals and homeowners. Near the beginning of each workshop, we try to make the point that graywater needs to be treated just like combined household sewage flows before it is released to the environment.

Early on, our rationale was based on observations by other professionals that one of the easy “fixes” for septic system problems and failures would be the homeowner running washing machine water out into the yard, bypassing the septic tank. This immediately removed pressure to the drainfield, oftentimes — at least from a homeowner perspective — “solving the problem.” When asked why they used this approach, homeowners say they heard from a septic professional that graywater was really pretty clean water and there was no danger to public health by discharging the water to the surface.

In recent years, this topic has taken on some different meaning with the move to segregate household waste streams to use water more efficiently and ensure water is recycled to replenish groundwater supplies. Questions at workshops have evolved to focus on the reuse of water for irrigation or somehow recycle it back through the residence or facility.

The concept of recycling and reusing wastewater is very good and deserves our attention. As the availability of good, clean water is reduced, pressure will mount on our industry to use different strategies in wastewater treatment and use. Reuse, along with reducing water use, will become a larger part of what we do.


We agree with some of the strategies employed for graywater management (not running it out to the surface direct from the washing machine, though). Graywater needs to be treated to avoid risks to human health. Along these lines, graywater may also need additional treatment before it is suitable for use in irrigation of ornamental plants due to the presence of nutrients and salts. Although this is important for irrigation purposes, the primary concern is the potential for pathogenic organisms to be present in graywater. As we like to say, this is the stuff that can make you sick.

Quite a bit of research has been conducted on this subject over the past 40 years. Graywater has been evaluated for the presence of total and fecal coliform, as well as E. coli and Streptococcus. The thinking on the part of professionals is that the majority of any pathogens present in the wastewater stream would be from the toilet waste and that graywater from bathing, laundry and even the kitchen sink would be much cleaner.

Graywater has fewer bacteria indicator organisms than toilet waste by itself or typical combined household sewage flows. In all cases, research has indicated the presence of fecal contamination, and when evaluated for common pathogens, they are also present.

The U.S. Environmental Protection Agency guideline for fecal coliform in reclaimed water for irrigation is set at 200 cu/100 mL. Published data shows suggested appropriate values for domestic wastewater recycling of <10,000 and <2,000 cu/100 mL for total and fecal coliform, respectively. While there has been a wide range of values, over time and by location, measured from research studies, these values are often exceeded. Bathing and clothes washing represent the two major activities to introduce pathogenic contamination to residential graywater.


Results of the microbiological studies have demonstrated that in both bath and laundry waste there is the potential to contain enteric (intestinal) and non-enteric organisms. While the levels measured are much less than toilet or combined household waste, direct human contact with graywater should be avoided unless the wastewater is disinfected.

A lot of the research on graywater has focused on the impact reduced levels of biological contamination have on treatment in soils. If the toilet waste is taken out of the waste stream, the size of the soil treatment part of the system can be reduced and potentially have less of a separation distance requirement. This is dependent on your state and local regulatory authorities, but we see more opportunities here than in the past. This is particularly true in areas where there is the desire to return as much water as possible through the soil to recharge groundwater aquifers.

While, it is clear that direct contact with graywater should be avoided for health reasons, there is not a consistent regulatory approach across the country concerning the type (chlorine, ultraviolet) of treatment or what level needs to be achieved before effluent is discharged directly to soil or water. If segregation and treatment of graywater is part of your approach or you think it will work for your clients, check your local regulatory requirements before proceeding.


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