Simple rules for simple uses of untreated grey water


The term "water budget" is making the rounds, so it may be useful to know a bit about recycling untreated grey water. What is it and how can it be used?

For the purposes of recycling water at home so as to reduce your fresh water consumption, water becomes grey and potentially useful without extra treatment after you have used it to wash clothes or people, according to Greg Smith of the San Mateo County Environmental Health Department.

The water is untreated if it has not been run through a system designed to decontaminate it.

Grey water from washing machines, bathtubs and showers is always contaminated with bacteria at higher levels than in the case of potable water. The county allows the use of untreated grey water for two purposes only, neither of which requires a permit from a city, town or county.

There are caveats. It must be used on the day it is collected. If it smells, that's a sign that it's become rancid and unsafe, Mr. Smith said. If you're collecting it in a shower or bathtub with a bucket, it's important to keep toddlers away from the bucket, which becomes a drowning hazard, he said.

With these safety precautions in mind, you can use grey water collected on that day to flush toilets. Just close the valve to the toilet's water supply, wait until the toilet's been flushed, then refill the tank with the grey water. Mr. Smith said he does this at home and has shown his children how to do it.

You can also use the day's collection of grey water to irrigate plants. It must be delivered to the plants from below the surface. Running it through a hose or a PVC pipe under mulch is a common way to do this, he said.

Grey water cannot be sprayed as irrigation and cannot be allowed to run down streets or driveways, form ponds, or be available to thirsty animals, Mr. Smith said.

Mulch degrades over time, so it is incumbent upon the resident to actively maintain the ground cover in order to properly distribute grey water under it.

The county Environmental Health Department is compiling a list of detergents and soaps considered safer when used in untreated grey water, Mr. Smith said. Generally, products with low phosphate content are safer, he said.

Rainwater collected from roofs or downspouts can also be used for irrigation, Mr. Smith said. There is no set limit on how long it remains useful. The state plumbing code has details on storing rainwater.

Rainwater that hits the ground or runs down paved surfaces such as roads or driveways must be treated, Mr. Smith said. The same applies to water from a kitchen sink, a dishwasher or a toilet.

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