Rooftop rainwater harvesting has been practiced for more than 4,000 years of human history, and still remains necessary in many areas where there is no centralized water supply system or when quality surface water or groundwater is lacking[sc:1]. Rainwater collection practices are becoming increasingly necessary around many parts of the world today, as drought events increase, and global climate change is altering precipitation patterns and rain events are becoming more variable.
Some advantages of rainwater harvesting
- Rainwater harvesting systems are generally easy to install and operate, and local people can be trained to construct and use them.
- Rainwater is a convenient water source at the point of consumption and allows for full local control, even at the family level.
- Rainwater has the potential to provide for a continuous water supply for those living in rural areas, as well as for the poor.
- Rainwater is generally considered to be suitable for domestic use.
- Rainwater harvesting systems have few negative environmental impacts compared to large centralized water supply projects.
- Water collection and storage capacity can be increased as needed to meet increased demand for water.
Some disadvantages of rainwater harvesting
- Rainfall can be limited in quantity and can be difficult to predict.
- It may be more difficult to convince government agencies to invest in such projects compared to a large centralized water supply project, as rainwater collection is generally considered to be a “bottom-up” and not a “top-down” type of project.
Costs of rooftop rainwater harvesting systems
Costs of rooftop rainwater harvesting systems vary based upon location, materials, size, and the type of system implemented.
Rooftop rainwater harvesting systems are useful for augmenting the water systems in both urban and rural areas, and they are excellent for use in arid and semi-arid areas where traditional water sources are not readily available.
Components of a rooftop rainwater harvesting system
There are three basic components of a rooftop rainwater harvesting system.
- Collection (Catchment) Area: In the case of a rooftop rainwater harvesting system, the roof of a house or of another building serves as the rainwater collection area. The efficiency and the quality of the water collected depends on the effective roof area and the materials that the roof is constructed of.
- Conveyance System: This is what connects the catchment area to a rainwater storage area. Conveyance systems typically consist of gutters or pipes that drain the water that is collected from the rooftop into cisterns or other storage containers.
- Storage Containers: These containers are typically in the form of a storage tank or cistern, but they can also be mortar jars, made from concrete, or they can even consist of simple vessels that are placed at the edge of roofs. The storage containers can be incorporated into a building’s construction, but also can be built on site separately from the the building. Storage tanks that use gutters can be placed above or below ground.
Whatever type of rainwater storage container is utilized, the water storage capacity needed must be taken into consideration, with factors such as the length of the dry seasons, the amount of rainfall, and the consumption of water needed per person.
Best practices and cautions
- All components of a rooftop rainwater harvesting system should be made of chemically-inert and non-toxic materials to keep the water quality from being negatively affected by chemicals. Examples of such materials include wood, plastic, aluminum, or fiberglass. Non-toxic paint should also be used if the roof or other materials must be painted (this means no lead-, chromium, or zinc-based paints). Also avoid any overhanging vegetation within the rainwater catchment area.
- To reduce the opportunity for bacterial growth, along with reducing the presence of dust, leaves, bird and animal droppings, and insects, be sure to keep all surfaces clean, including all drains and roof surfaces. If the rainwater is to be used for drinking, it will need to be filtered and chlorinated or disinfected by another method (such as boiling).
- Storage tanks need to have a tight and secure cover that will keep algae from growing and mosquitoes from breeding in them. An effective cover will also keep the water from contamination from humans, animals, and other environmental contaminants. It is not recommended that open containers be used to collect rainwater that will be used as drinking water.
- Storage tanks should be checked and cleaned periodically. The design of the tank should allow for ease of cleaning. All surfaces of the tank should be cleaned and scrubbed, including the walls and the floor. Dirt, leaves, and other materials may also need to be removed from time to time.
- Inspect the storage tanks regularly for cracks and repair if necessary as soon as possible to avoid major problems from developing later on. An optimal time to inspect the tank for damage is prior to the beginning of the rainy season.
- Chlorination of the cisterns or storage tanks may be necessary for drinking and domestic use of rainwater.