We have high and pretty reliable rainfall in our area and have decided to use harvested rainwater as our backup supply.
Here are a few things we have discovered so far:
Water is heavy stuff: 1kg / L so siting of rainwater tanks needs to be carefully considered.
Gravity: Bearing in mind the weight, siting the tank high up is desirable as it will allow the content to be gravity fed. As the rain is collected from roof height, siting the harvesting tank as high as is structurally safe creates a good head of water without the need for pumping.
Contamination: Rainwater is not pure and uncontaminated. It picks up debris from the air as it falls as well as from the surfaces it falls onto. It is mainly the contamination from the surfaces it falls on that are of concern. These can range from heavy metals from lead and copper roofing to pathogens and bacteria contained in bird shit and decaying organic matter on the roof.
Filtering and Sterilising: We will initially be using a simple sand filter to remove coarse debris for normal domestic needs, then the Berkefeld system for stage 1 of drinking water supply. Stage 2 of which will be by boiling to kill any remaining pathogens.
Storage:
Light: We will be using an industrial grade PE tank reservoir. It is thick translucent material that lets light in. This is a problem as light promotes the growth of algae and other undesirable organisms. So, it is important to site reservoirs away from daylight.
Freezing is another problem we have considered. I have read that straw bale insulation can work very well here. The tank we have ordered is 1000L so will have a fairly good thermal mass we hope, so we’re going to give the straw bale insulation a try.
Concrete base issues: Scythe has written of problems of contamination caused by letting PE containers sit in direct contact with concrete flooring for prolonged periods. We have not found mention of this anywhere else, but just to be on the safe side we will be insulating our reservoir from the concrete floor by standing it on a platform of engineering bricks.
A good downloadable Pdf about raiwaterharvesting of drinking water can ne found at:
http://www.rainwaterharvesting.co.uk/......pdf‎
Thoughts, comments and advice always welcome. ïÂÅ
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