Rooftop rainwater harvesting in Nepal
IntroductionRural communities are often unaware of the benefits of rooftop rainwater harvesting and are not likely to construct such systems on their own initiative. Locally available materials and labor can be used to construct the jars, but institutional support is necessary in order to provide technical inputs, raise awareness of the benefits, and provide support on construction and maintenance techniques. Rural communities play a central role during project implementation, but in contrast, their role during the pre-development phase is somewhat limited.
Operation and maintenance expenses are low, in fact, on average every household spends US$ 3,5 and 6 hours per year on maintenance tasks in the system. Although rainwater still requires boiling before drinking, it is healthier than other drinking water sources, especially during the monsoon.
In terms of benefits, every household saves on average 6.4 hours per day in water fetching, especially women and girls. Most women employ the time saved in reproductive activities, such as taking care of the children, cooking or cleaning, or on income-generating activities, such as selling of vegetables from the kitchen garden and livestock. Women have also more time available to participate in social and management activities such as studying, training or accounting. Major availability of water is also directly related to better hygiene practices and an improvement in health conditions in communities.
ObjectiveThe objective of this practice is to ensure water availability for drinking and irrigating kitchen gardens at a time when overall water availability is low.
Implementation of the TechnologyA rainwater harvesting system consists of three basic elements: a collection area, a conveyance system, and storage facilities (Figure 1). The collection area is the roof roof of the house, solid enough to shunt rainwater efficiently and to install a gutter system. The conveyance system usually consists of gutters or pipes that deliver rainwater falling on the rooftop to the storage facility. (Figure 2)
Implementation of rooftop rainwater harvesting system requires substantial initial investment of time and money from households for acquisition of materials, jar construction training and labour, transport of jars to homes, and home installation of jar and gutter system.
The following questions need to be considered in areas where a rainwater harvesting system project is being considered:
- Is there a real need for an improved water supply?
- Are present water supplies either distant or contaminated, or both?
- Do suitable roofs and/or other catchment surfaces exist in the community?
- Does rainfall exceed 400 mm per year?
- Does an improved water supply figure prominently in the community's list of development priorities?
If answer to these questions is yes, a rooftop rainwater system is a feasible water supply option. Further questions, however, also need to be considered:
- What alternative water sources are available in the community and how do these compare with the rooftop catchment system?
- What are the economic, social, and environmental implications of the various water supply alternatives (e.g., how able is the community to pay for water obtained from other sources; what is the potential within the community for income generating activities that can be used to develop alternative water sources; does the project threaten the livelihood of any community members, such as water vendors?)
- What efforts have been made, by either the community or an outside agency, to implement an improved water supply system in the past? (Lessons may be learned from the experiences of the previous projects.)
All catchment surfaces must be made of nontoxic material. Painted surfaces should be avoided if possible, or, if the use of paint is unavoidable, only nontoxic paint should be used (e.g., no lead-, chromium-, or zinc-based paints). Overhanging vegetation should also be avoided.
Rainwater harvesting jars vary in size and costs. The financial cost of a 2,000 litre ferro-cement jar (Figure 3) and gutter system ranges between NRS. 6 000 and NRS. 8 500 (US$ 80 - 110). Costs depend upon delivery fees, which vary according to the number of jars delivered to one locality and the distance of the construction site to the road network, but could also vary according to construction materials.
A rainwater harvesting jar of 1 000 litres is the minimum size recommended for a household of 2-4 individuals, since rainfall can be sporadic. Harvesting water from a roof area of 20 m2 could meet all drinking water needs of a family of 2-4 people from June to September (monsoon), and 30, 80, and 40% of the total water needs in April, May (pre-monsoon), and October (post-monsoon), respectively.
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