Designing an Oasis with Greywater

Introduction
Most greywater industry offerings are elaborate systems featuring filters, pumps, tanks, valves and sometimes disinfection and electronic controllers, etc. They cost from $1000 to S30,0OO (gasp!) for a single-family residence. The vast majority of these are either newly installed, or abandoned, or failing to meet their original goals. However, these are a small percentage of the systems in use: 5% or less.

What about the other 95%? Many have beer working for decades without the users' even thinking about them. The majority consist of nothing more than a drainpipe pointing down the nearest hill. The classic 'drain out back" has some serious shortcomings, but its durability and spectacular simplicity give one serious pause for thought.

From a holistic ecological design perspective, a really complicated, expensive system is doomed from the start. At best, all it can hope to do is shift the impact from the waste or water to the waste of resources used to make pumps, valves, tanks, piping and electricity.

How about scrapping all this delicate, expensive technology which is nearly impossible to make ecological, affordable, or durable, and instead concentrate on improving the humble "drain out the back?" What does it have to teach us?

"The drain out the back"

Advantages of the "drain out back"
+ No filtration necessary
+ No pumping necessary
+ No surge tank necessary
+ Little pipe is needed
+ Little or no required maintenance
+ Low economic and ecological cost
+ It can be built by anyone
+ Low failure rate (that is, they are little worse in year 100 than year one)
+ They last forever

Drawbacks of the "drain out back"
Low reuse efficiency
With all the water dumping in one spot, the result tends to be over watered patch and everything else under watered. Usually nothing is planted to utilize the water, in which case the reuse efficiency is zero. If the flow is high, plants at the outlet might be able to utilize only a fraction of the water available. In a few lucky instances there is a fruit tree which grows until its water need equals the available flow, in which case the reuse efficiency is close to 100%.

Poor sanitation
Without a basin to contain it and mulch to cover and slow it, greywater applied to the surface from a "drain out back" could flow into a creek, onto the street, or whatever, especially if it is raining. In older installations near natural waters, the pipe typically discharges directly into them.

Without mulch or soil covering it, greywater could be lapped up by dogs, played with by children, or prowled for food bits by vermin. This litany sounds worse then it really is in most first-world installations (where not a single case of greywater transmitted illness has been documented). Amazingly, wastewater just flowing over the ground for some distance (say fifty feet) receives spectacularly high treatment by the same beneficial bacteria that live in soil.

In third world countries, especially in shanty towns where people live in appalling intimacy with their greywater, it is just as bad as it sounds above.

Soil overload/poor aesthetics
With a typical "drain out back," a mucky, anaerobic grey-white material on the ground indicates where the soils purification capacity is overloaded. This patch can measure from a few inches to several feet in length. If it slopes so the greywater runs off and infiltrates into the surrounding soil, there is usually no odour unless you stick your face in it. If the greywater pools at the outlet, odour is likely, and mosquitoes are possible. Some plants may he harmed by root suffocation.

Illegal
Though common throughout the entire world, the "drain out back' is illegal, primarily because the the effluent is applied to the surface (this virtually never results in official censure with existing structures, but it wouldn't be permitted for new construction or a remodel).

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