Monday, 27 February 2017

Water harvesting system

My father put in a water harvesting system when he built his house twenty years ago. It still seems to work. Last time I visited, I helped my mother change the filters and clean out the gutters. Actually we should have done that the other way around. While cleaning the gutters, a certain amount of crap ended up washing down the gutters, and straight into the nice clean filter, so if you ever find yourself cleaning a water harvesting system, clean the gutters first!

​Three drains from the house, and one from the garage to the right, all come into one gutter. This then heads through a drainpipe into the filter butt.

Water goes through a grill to catch leaves and large debris, then a felt filter bag lined with a nylon gauze bag. The filter butt can take something like 100 litres, which quickly fills up if it is raining heavily since the roof has a large area, and it takes time for the water to get through the filter. Another piece of advice: it's a good idea to change the filter when it has not rained for a while, then it is a lot lighter.

When you don't need any more water, the large yellow pipe to the right of the filter butt can be put onto the drainpipe to bypass the filter. In fact when changing the filters, we should probably have put the bypass pipe on.

Filtered water then goes into a tank under the garage. There are two tanks, one being filled and the other supplying water to the house. You can choose which tank to fill by putting the hose into it, and the red taps will choose which tank is supplying water.
Wonderfully low-tech!

You can see how much is in each tank with these two old washing-up liquid bottles, filled with sand, which have floats attached to the other end of the strings.

Detailed calibration has been added.
An electric pump draws water from the tanks, either on demand from a float in a tank at the top of the house, or at the flick of the "over ride" switch.

From the pump the water goes through a chamber with a purification tablet on the left, then another filter on the right.

The pipes then run along the wall to another clearly laid-out junction where the harvested rain water can be switched off, and mains water can be switched on instead. The pipe goes into the house and up to a water tank above the bathroom, which has a ballcock that activates the pump when more water is needed.

This system still works after twenty years, providing most of the domestic water. There are a couple of separate taps of mains water in the house for drinking and cooking. I particularly like the layout and simplicity of this system, and if anything did go wrong with it, any handyman could quickly work out what was wrong and how to fix it. Financially it has probably not paid for itself, since their water is relatively cheap, and in fact my Dad admitted it was a bit of folly, but I'm sure he enjoyed making the system and was very satisfied to see it work.

It does provide some insurance against water shortages, which may now happen with increasing frequency, in and amongst the increasing floods! In many areas there is a cheap, regular and safe supply of water, and harvesting your own water is probably a low priority if you are building on a budget. Rain water harvesting is now mandatory in some Indian and Australian states, and many places around the world offer financial support for people harvesting water. And if you are building on a plot a long way from the infrastructure then a rain water harvesting system could save money.