WATER WISE
Filters that work on common sense
S. VISHWANATH
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The filtering process should not result in choking and consequent flooding
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Simple: A do-it-yourself rainwater filter
Now that rainwater harvesting has swung into action in a big way in our cities, it is important to understand one critical component of the system, the filter. The entire rainwater harvesting system consists of a catchment, which is usually the roof; the conveyance, which are rainwater gutters and downpipes; the filters, (more about that will follow in detail) and finally the storage or recharge, which is a sump or a well.
What is the role of a filter? It's primary job is to keep organic particles and silt out of the rainwater to be harvested. Since a filter has to handle a heavy downpour at times it cannot function at micro-filtering the rain. It can only keep the larger particles free.
What filter is good? There are many in the market and most of them do the basic job of keeping organic particles out. They should also be easy to maintain and to clean. Self-cleaning ones are yet to come into the market. The filtering process should not result in loss of rainwater to be collected or should not also result in choking and consequent flooding. They should also be cheap and easy to replace.
Simple mechanism
For individual homes, a simple drum with a cloth covered inlet is good enough. That is provided the roof catchment is kept clean and does not have heavy leaf litter. Passing the rainwater through a sand bed is simple and easy. For a 100 square metre roof area, one 60-litre drum filter is usually enough.
The filter, if made of ferro-cement, can last longer and is much tougher than plastic. Ferro-cement does not crack in the sun and is much more eco-friendly than PVC.
A bye-pass system helps in the filtration process because it is only the first 5 mm of rain which usually needs to be cleaned.
Before buying and installing a filter, ask what it does. What is the difference between input and output water quality and how easy is it to maintain?
Go for the simpler and tougher ones and at all times remember that the rainwater quality is most improved by a clean catchment.
Water wisdom lies in using common sense and keeping things simple but with a clear understanding of requirements.
www.rainwaterclub.org
zenrainman@gmail.com
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