#701Domestic rainwater harvesting (rooftop catchment)
701⸱AConcept
- Saves water resources
- Provides water for household use
- Provides water for small-scale use in agriculture
Domestic rainwater harvesting is a method of collecting rainwater, storing it, keeping it clean, and using it for household purposes such as bathing, cleaning, washing clothes, livestock or growing vegetables, and in some regions also for cooking and drinking.
Rainwater is collected on the roof – only rooftop collection is classified as clean for direct domestic use – and transported with gutters or channels to a storage reservoir, where it provides water at the moment of consumption. Other forms of collection are indicated for use in agriculture and livestock as well as other purposes except for consumption.
It is a simple technique that offers many benefits, such as a constant supply of clean water throughout dry periods and easy access to it. It reduces the daily burden of women and girls, who are in many countries the ones fetching water from common water sources and carrying it over long distances. Rainwater harvesting relocates the water source directly to where the water is needed.
701⸱BTo be considered
The cost of the setup or construction needs to be considered. There is a variety of systems of different materials, shapes, and sizes, above ground or underground, and serving different purposes. In the further reading section below, you find a manual with information on what to consider and how to install the different systems. Here in this tool, we present the setup of a system using a plastic tank as a water reservoir for human consumption.
Most domestic water harvesting tanks are available in local hardware and fabrication shops. Plastic tanks have many advantages: They are readily available, lightweight and easy to transport and install, they last for more than 30 years and are easy to clean, they have little maintenance cost and no leakage as there are no joints. Metal tanks or masonry tanks constructed by masons can be an alternative.
The required size of the tank needs to be considered: Avoid a tank that is too large and never fills or one that is too small and always overflows. The tank should be sized to provide enough water for a dry season of about 3 months. The demand should be calculated based on the purpose, the number of household members, and the daily consumption. The daily consumption should be known to calculate the required size. In Brazil, the daily consumption is around 120 liters per person.
The tank should always be smaller in height than the building on which the water is collected. In that way, all rainwater can be drained away from the gutters.
A first-flush system should additionally be installed as it leads the first amount of rainwater away from the tank to provide for more cleanliness of the water inside the tank. One form of a first-flush system can be a vessel between the collection building and the tank which fills up first. The water collected here is non-potable and can be used for irrigation, e.g.
The harvested water that is drawn from the tank should always be boiled or disinfected with chlorine to make it safe for drinking.
Domestic rainwater harvesting can serve as an additional income source if the water is sold to neighbors and community members. Also, it facilitates the production of vegetables in the garden that can be sold and contributes to the family’s nutrition. All forms of commercialization or business activity must, of course, comply with the local law.
Timing: The domestic rainwater harvesting system should be set up before the rainy season starts.
701⸱CImplementation
For more detailed implementation instructions and a comparison of different systems, please follow the links and materials in the Further Reading section below.
Materials
701⸱1Preparation
701⸱2Procedure
Preparing the tank
If required, the pipes should be supported so that the tank walls are not under too much stress.
701⸱3
701⸱4
Installing the gutters
Position the gutter so that the brackets fall in the center of the overlap for added support.
701⸱5
Tank for human consumption
701⸱6Application
If there is no first flush system in place or maintained correctly, the tank should be cleaned every three months or at least at the beginning of each rainy season. Gutters and covers should be cleaned after leaf fall, and drain pits should be cleaned at least once a year.
701⸱7
Avoid standing water as this can facilitate the breeding of mosquitoes. If more water runs in than the tank can hold, make sure that the overflow system is working or divert the downpipe away from the system.
701⸱8
The water drawn from the tank should always be boiled or disinfected with chlorine to make it safe for drinking. This precaution is not necessary if the water is only used for irrigation or other household purposes.
701⸱9
The water level can be checked using a long, clean stick pushed straight through the tank from top to bottom. After pulling it out, one can see the level of the water from the part of the stick that is wet. Another way is by knocking on the side of the tank from top to bottom if it is a plastic or metal tank. By listening for a change in sound one can estimate where the water line is.
Saving for and installing additional gutters, if the roof can take it, can make the system more efficient. Especially towards the end of the wet season, when rains are less frequent, there is a need to catch as much water as possible so that the tank is full at the beginning of the dry season.
701⸱10
Don’t climb on the top of the tank, as the additional weight might damage it.
701⸱DEconomic benefits
Time saving
This tool saves time and effort in day-to-day life.
Health cost saving
This tool can help reduce disease-related costs, such as health care costs or productivity losses.
Better nutrition
This tool provides for a better nutrition of the whole family and therefore saves cost of health care.
Higher coffee yield
The effects of this tool can lead to a higher coffee yield and therefore a higher income.
Additional income source
This tool has the potential to provide an additional income.
701⸱EGreen benefits
Water saving
This tool saves water as a scarce resource.
More water availability for irrigation
This tool provides water for irrigation not only of coffee plants but of seedlings, vegetables, different companion trees and other vegetation types.
Balances the local microclimate
This tool helps to grow diverse plants which help to balance the local microclimate. This helps mitigate several effects of climate change.
Higher biodiversity
This tool helps form habitats for different plant and animal species to grow. This contributes to a healthy ecosystem.