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Are you a professional working in WASH, water supply or agriculture? And are you looking for alternatives to conventional ways of water supply to make your project more sustainable, or do you have problems with the availability of water resources in your project? Then this tool is designed for you!

This tool provides you with practical information on rainwater harvesting and shows that rainwater harvesting is a viable alternative and an addition to conventional ways of water supply. It allows you to estimate how much of your water needs can be covered by collecting and storing rainwater, and which techniques might be most appropriate.

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Rain is Gain Tool

Discover what the potential of rainwater harvesting can be in your project. Go through the steps below, fill in your water needs and calculate your potential of rainwater supply. The Rain is Gain tool provides you with an estimate of quantity of rainwater that could be generated by various rainwater harvesting techniques in your project area. It helps you determine whether or not this is enough to meet your water expectations, including different solutions.

  • First, let’s calculate your water needs: the amount of water needed for different purposes - from domestic to productive.
YOUR WATER NEEDS (scroll to middle of page)
  • Now let’s calculate your water supply: the amount of water that can potentially be generated by different rain water harvesting techniques in your project area.
YOUR WATER SUPPLY (scroll to middle of page)

What is Next?

Explore rainwater harvesting technologies and techniques.

Rainwater Harvesting pages.

Broader Context

Each decision on rainwater harvesting is context specific. The characteristics of the landscape, people's needs, local practices and laws & legislation differ in each country or catchment area. This can significantly influence your project. Therefore, when thinking about incorporating rainwater harvesting in your project, it is useful to take into account the following five aspects:

The Landscape Water harvesting can be planned and implemented at different scales: from isolated individual plots within fields up to schemes covering a whole watershed or landscape. Water harvesting deliberately reallocates water resources within a landscape. Water sources in your project area may include springs, rivers, lakes, wetlands, rainfall and groundwater. It is important to have a clear understanding of the location of these sources, their availability throughout the year, their quality and their use. Bear in mind that the water flows and sources within a landscape are interconnected and affect one another. For instance, if you plan a storage dam at a specific location, people living downstream might receive less water.

At the same time, a landscape provides different kinds of services to its surrounding communities. Healthy ecosystems directly feed vulnerable communities. A forest supplies people with food and water; trees on slopes regulate floods and increase water infiltration; and wetlands and forests have water-purifying functions. Make sure that you are aware of these different services.

Check out this tool to learn more about environmentally sustainability within WASH projects.

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Water Quality As many public health problems are caused by contaminated water, it is important to make sure the harvested water used for drinking is of acceptable quality. Take into account not only the potential effect of natural processes (leaching, weathering, and dissolution) and human activities (agriculture, industry) on water quality, but also be aware of, for example, mosquitoes breeding in or near rainwater harvesting systems. More information on water quality issues related to rainwater can be found in the RAIN Water Quality Guidelines. Water quality icon.png
Social Sustainability Projects are socially sustainable when they do not hinder a person from having access to water and when all stakeholders involved can voice their needs and expectations within the project. Ideally this should happen in the project design and planning phase. A socially sustainable project takes into account gender, age, economic status, social position, religion and culture. So before setting up a Rainwater Harvesting project, include these aspects in your work. Social sustainability icon.png
Multiple Stakeholders Involving organisations from different sectors in your project, such as governmental organisations, the private sector and NGOs, is very important for its success. Be aware of the fact that every organisation has different roles and responsibilities. It will increase the institutional sustainability of the project if each party can, and is prepared to play its role. Facilitating a so-called enabling environment by using a multi-stakeholder approach should be part of your project design planning. Try to get a better understanding of local laws and regulations, and invest in involving all relevant stakeholders that could support your project. Multiple stakeholders icon.png
Finance Financial sustainability lies at the foundation of any successful project. People must be able to invest in a project to increase ownership and to keep the project running in cooperation with (local) governments and the private sector in your project area in the long term. Ask yourself important questions: can your project be financed locally? Are there banks or other (micro) financial institutions that can support your project? And will the project lead to increased income generation? Finance icon.png



RAIN brings 10 years of hands-on rainwater harvesting experience and extensive knowledge in project and program design and management. RAIN can give you access to a wide international network of implementers, policymakers, networkers, experts and other partners. If you want to know how to design, coordinate, manage, monitor, evaluate and/or promote your initiative on rainwater harvesting, we’ll gladly stand by your side and provide insights and solutions.