Grey Areas of Greywater Recycling

Even in households that make a concerted effort to conserve water, much of it ends up going down the drain. Rowan Watt-Pringle profiles the issues surrounding the reuse of this so-called greywater.


When examining the use of greywater (post-dishwashing and bathing water) it is important to make the distinction between it and blackwater (toilet wastewater).

Combined wastewater contains a lot of nitrogen, one of the primary pollutants affecting any potential drinking water, but 90% of it is found in blackwater. Toilet waste can also contain dangerous pathogens, while greywater pollutants decompose faster, reducing the chance of water pollution.

Discharging greywater: keep it simple

According to Richard Jennings, designer at Santa Fe-based Earthwrights Designs, household greywater does not usually need to be filtered or decontaminated.

"The simplest way to deal with the greywater is to discharge it through large orifice pipes," explains Jennings. "Some other practitioners filter and disinfect with chlorine, which can perhaps be useful in urban high density situations."

CC Pereira, founder of environmental website eco-nomics.info, also believes simpler is better when it comes to designing greywater systems. "I prefer to stick with the simplest, cheapest, most effective methods possible," says Pereira. "The more accessible essentials like clean water, healthy foods and homes are to people, the better."

"Jennings believes there is still a lot of work to be done in the US when it comes to regulating the reuse of greywater."

Continuing in this vein, Pereira explains, "The basics [like food, water and shelter] have never had to be created, manipulated, modified or 'technified' before. I believe these things should remain this way, so that they remain available to the general public.

"Greywater recycling should definitely become a far more important part of daily life," Pereira continues. "It can be reused for the lawn, garden, orchards and so on - even if only to supplement their water sources. Since water is going down the drains every day, one can rest assured that the garden is getting the water it needs."

Pereira advocates a simple, non-galvanised mesh screen to filter out debris, cautioning that "the mesh should not be made of or coated with toxic or heavy metals such as aluminium, hexavalent chromium or lead".

Other filtration systems

Soilboxes have been successfully used to purify greywater since 1975, with a bottom layer of polyethylene "actifill" or pea gravel for drainage to prevent water-logged zones.

Willa Eco-matic is a replaceable filter technology from Finland, consisting of a fibre and ion-exchange media within a sack, while sand beds with geo-textile cloths and leaching boxes attached to pumping systems can also be used.

Greywater: significant potential savings

According to Jennings, "Greywater accounts for 60%-70% of indoor household flows, so how it is used and what water source it replaces will determine the financial savings people can achieve."

He adds that financial savings are not the only potential benefit to be gained from the re-use of greywater: "Another important consideration is that water delivered to your tap has embodied energy from extracting, treating, pumping and maintenance of infrastructure. So the use of greywater also provides savings of both water and energy."

On a similar note, Pereira says, "Considering that most of the water going down our drains is greywater and very little of it is used for drinking, using a greywater system could theoretically save most of one's water bill."

Greywater regulations

Jennings believes there is still a lot of work to be done in the US when it comes to regulating the reuse of greywater - and that the power to effect positive change rests with the general public.

"In the US, we have a corporate media controlled by people living in fear and greed," asserts Jennings. "The result is the attack on what environmental policy we have achieved by the propaganda machine that poses as news," he continues, "but people have shown in the past that they will try to do what is good for them. Most of the laws that accept greywater use have resulted from widespread civil disobedience."

Jennings cites the law in New Mexico as an illustration of how adequate greywater safety can be achieved by using common sense and simple techniques.

The law allows private, residential greywater discharge of less than 250gal a day to be used for outdoor irrigation, subject to a number of stipulations.

"Household greywater does not usually need to be filtered or decontaminated."

These caveats include - among others - either the presence of a constructed greywater distribution system providing for overflow into the sewer system or an on-site wastewater treatment and disposal system; that greywater is only used on the site where it is generated; a 5m vertical separation between greywater and the groundwater table; and that greywater is not stored for longer than 24 hours before being discharged.

Jennings explains the reasons behind the latter stipulation by pointing out, "Storing greywater beyond 24 hours creates the same biology as an anaerobic septic tank."

Greywater reuse indoors

While the mesh screen is adequate for recycling greywater outdoors, if one is planning to reuse it for drinking, bathing and other indoor needs, Pereira also advocates the use of a ceramic water filter.

"Ceramic filters can be reused by scrubbing off layers over time. They are simple, affordable, non-toxic and environmentally friendly," he explains. "You can also add some UV purification, which is often included as part of a purification system."

A change in lifestyle

The reuse of greywater can be supplemented by a change of lifestyle to focus on savings and environmentally friendly living by incorporating systems such as compost toilets and rainwater tanks.

According to South African website freewater.co.za, more than 3,500 houses in Cape Town already use greywater to water their gardens every day, while in the US city of Santa Barbara, California, 40% of the 200,000-strong population use greywater systems.

It appears that people the world over are coming round to this new, more responsible way of life, with greywater replacing fresh water in many areas where irrigation is needed - saving money and increasing the effective water supply.