Rooftop rainwater harvesting utilizes roof surfaces like metal sheets, tiles, plastics to divert the flow of rainwater with the help of downpipe and gutters, to preserve it for future use. The system being used can be anything, ranging from a bucket to a seven hundred cubic meter subterranean storage tank. The water collected in this procedure is rainwater which in itself is not highly contaminated in the first place. So even if it contains salt or arsenic still, it can be utilized for sanitary purposes and even washing in some cases. It can play a role in helping separate buildings to be able to manage their personal supply of water for domestic use, drinking water, and economic activities.
Does it Work?
In countries like Sri Lanka and Uganda, there is a long going tradition of rainwater preservation from trees. In their procedure, stems or banana leaves play the role of temporary gutters.
Rooftop rainwater harvesting can be done in all kinds of climates. But of course, it is more fruitful when it is done in wet and rainy regions. Whenever there are dry periods then to fulfill the water requirements some system of storage of water has to be maintained. If the designing and maintenance of the system are done carefully, then the collected rainwater meets the quality standard for drinking water.
How to do it?
Building rooftops are mostly constructed with Reinforced Cement Concrete or RCC, which have the prerequisite that rooftop rainwater needs to be drained outside the plot area. Instead of letting this water to runoff or be lost by evaporation and percolation this water is stored and used on the roof or the ground surface or underground.
Different aspects of this system include
Roofs can either be of the flat or the sloping form. Flat roofs constructed with reinforced cement concrete or RCC have their surface finished with an efficient waterproofing course. It is slightly sloped towards the pipes that take the water down. Nowadays rich cement mortar is used, either with or without weatherproof tiles. These provisions make such roofs excellent for rooftop rainwater harvesting.
Downpipes are used, to transport the rainwater collected from the ceiling to the filtration system, which can be made up of cement pipes, PVC or HDPE. The size of the down pipe varies depending upon the roof area to which it is connected.
The collected rainwater is not dirty, but contaminants like (dirt, bird droppings, leaves, etc.) get mixed up with it. So there is a need to filter this water before storing it. The filtration systems that are used can include
● Popup filter
It has three components which are
Rainwater receptor which is the part from where the rainwater flows through the downpipe.
Then the water reaches the flush valve, which flushes the first movement of rainwater which is mixed up with dust, leaves, etc. The water here flows up against the force of gravity where it reaches a filter element.
The filter element is the place where a maximum number of floating elements are filtered. It also facilitates the stabilization of water in the filtration zone.
● Sandbed filter
This traditional method allows rainwater to enter at one end, and this water is filtered by passing it initially through riverbed sand followed by pebbles, and, in the end, through aggregates. Clean water is collected from the other end.
Some storage structures which can be used are,
- Ferro-cement tanks
- Masonry tanks
- Plastic or metal tanks