Monday, 14 July 2014



Simple interventions on your roof can help you harvest rain. Here’s how
In cities, buildings are usually constructed with rooftops of Reinforced Cement Concrete (RCC), Mangalore tiles, asbestos / galvanized iron / zinc sheets etc. Rooftop rainwater usually flows into storm water drains outside the plot area. As roofs are built with hard material, large quantities of rainwater runoff and loss due to evaporation and percolation are minimal.  So, rooftop rainwater is just waiting to be harvested. You can either store rooftop water on the roof itself, at ground level or below the ground, using storage devices like masonry tanks, ferro cement tanks, or plastic / metal containers.

The process
Collection: Roofs can be broadly categorised into flat roofs and sloping roofs.  Flat roofs with RCC have water proofing on the surface as a surface finish. This surface is provided with a slope towards the down-water pipes.  For efficient collection and effective usage, the roof needs to slope towards the storage device. This will minimize pipe length to the storage system.  
Sloping roofs with RCC, Mangalore tiles, asbestos sheets or steel sheets lead the water to the lower edge of the roof. A gutter made out of sheet metal or PVC has to be installed at the lower edge to collect and channel water to the down-water pipes.

 Channeling: Down-water pipes made of PVC, HDPE or cement, can be used for transporting rainwater collected from roofs to the filtration system before storing. The size of the down-take pipe varies depending on the roof area, which is connected to the down pipe.

Filtration: Rainwater collected on the roof is very pure and clean.  However, there are many substances, which may contaminate this water such as leaves, bird droppings, dust etc.  These contaminants need to be filtered before the rainwater is stored.  There are many filtration systems such as sand bed filter, PopUp filter and stabilization tanks.
Sand bed filter: Sand bed filter is the traditional method of filtration where coarse riverbed sand, pebbles and aggregates are filled as layers, one above the other, in a confined masonry structure. Rainwater is allowed at one level and filtered water is drawn from the other.
PopUp filter: A simple PopUp filter works effectively for residential buildings and smaller institutional or industrial applications. It has three components – rainwater receptor, flush valve and filter.  

Stabilization tanks: Rainwater is allowed to flow through a series of small tanks and, by providing an entry and exit for water at strategic positions, impurities are trapped in the stabilization tanks for subsequent cleaning.

Cost is determined by:
                     * Quantity of rainwater to be collected
                     * Type of surface from where rainwater is collected
                     * Existing structure and fittings for rainwater collection and flow

                     * Type and capacity of harvested water storage device