In the earlier article, we discussed how water used for bathing and washing clothes can be treated by water-loving plants and allowed to percolate into the soil to augment the shallow water table. This concept can be used in individual houses. In apartment complexes, a large volume of greywater is generated and can be recovered for flushing, gardening and the excess water can be sent back into the soil. For this, a bathtub-like cemented structure has to be built with a sloping bottom with an outlet at the lowest point. A layer of blue metal is laid at the bottom with a small layer of sand over it, followed by another layer of garden soil. The Canna indica (Indian shot) is planted on the soil and a small inspection tank is provided alongside. The blue metal layer enables the treated water to freely flow out of the tank. The sandy layer prevents the soil from clogging the blue metal, while the soil layer cleans the water. The bottom can either be cemented or covered with a double layer of empty cement bags.
To utilise this water, we have to provide a three-compartment overhead tank (OHT). Builders generally provide a two-compartment OHT, one to hold potable water and the other to hold water for non-potable purposes. However, the potable water accounts for only 10-15 per cent of our total water usage and providing 50 per cent capacity for it is not necessary. Instead, a three-compartment OHT can be built in the same space that stores water for flushing, drinking and other purposes. By simply closing the two valves interconnecting the three compartments, we will be able to store three different qualities of water and use them for specific purposes.
In such an OHT, the treated greywater can be safely stored and used exclusively for flushing. Alternately, by closing one of the two interconnecting valves, two kinds of water can be stored and used appropriately. In such complexes, advance planning for recycling can be done by providing additional gullies for diversion of the greywater to the soil bed and connecting them with the normal gully through elbows and pipe pieces without applying any gum so that they can be disconnected whenever necessary and the greywater can be allowed to go into the regular internal sewage line.
This recycling method can be fully or partially decentralised wherein some of the greywater is cleaned and allowed to seep down to charge the shallow water table and the rest is treated and used for flushing and gardening.
Chennai-ites do not realise that in most parts of the city, the soil is suitable for traditional shallow dug wells. If such wells are provided, people will be able to enjoy greater water security as shallow wells generally yield good quality water, can be easily charged with terrace rain water and the excess water, not needed for flushing, can be treated and routed back to the soil.
This is the final of a three-part series on greywater recycling. For details, mail isragade@yahoo.com
