NOTE: Make sure you read the first three posts (in order!) before tackling the rest, or it could be confusing: Post 1 is Designing the future, Post 2 is Setting up the problem, and Post 3 is Estimating basic requirements.

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Friday, September 08, 2006

A sewer-less future...

This is the first of many posts I’ll have on grey water recycling. Grey water is essentially all wastewater that doesn’t need a toilet (that’s known as black water). Most buildings discharge grey water into the sewer or septic system, but there are concerns with both methods. First, post-peak, how reliable will your city sewer/water treatment system be? Second, running less waste through a septic system means less demand on that critical system. And in both cases why waste such a large quantity of water that, when properly handled, can be used for irrigation?

The fundamentals of grey water recycling are not difficult to understand, but nevertheless there are so many examples where people implement it all wrong. For a stellar resource on the topic, try Oasis Design. As this post is only an introduction to grey water systems, I’ll focus on some key concepts to keep in mind when designing. We’ll work on sizing such systems later.

1) Grey water is not clean water – Seems obvious, but it's somewhat more complicated than you might think. Grey water can be applied directly some trees, but should not be used to directly water lawns or gardens. This can be accomplished using subsurface irrigation.

2) Grey is not poisonous water – While grey water should be handled properly, it is unlikely to make you sick. Plants you water with grey water are safe to eat (provided you don’t water the edible parts directly). And remember, the only chemicals in grey water are the ones you put down the drain.

3) Avoid pumps and filters – This is especially important for post-Peak Oil considerations. Pumps will break down, filters will clog. Use nature’s services: gravity and soil filtration.

4) Avoid storing grey water – Grey water is the byproduct of your laundry, showers, baths, and cooking; as such, it contains dirt and bacteria. If left in a holding tank for more than 1 or 2 days, these bacteria will frolic and putrefy. Your system should rapidly discharge into the soil.

5) Don’t over-design – Grey water recycling can be as simple as emptying your bathtub by bucket or a single discharge line into the soil. Your level of design should correspond to your maintenance availability, irrigation needs, and actual water usage.

In short, grey water recycling can have tremendous impact on your overall water budget. It can allow you to relax the requirements on your water collection system and help with growing your plants when it's designed carefully and implemented properly. More to come on this in the future…

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