Rainwater Harvesting Systems

Module 3 – Designing your Rooftop Rainwater Harvesting System

In this module, you will learn

• how to calculate water demand
• Estimate water supply from a rainwater harvesting system
• Use this data to make design choices

This module would be helpful for you if you are interested in how to build a rainwater harvesting system for your own house or your community. It is assumed that you have the 1) basic understanding of climate, weather, and rain; 2) the ability to calculate the volume and surface; and 3) the ability to understand the appropiate size of the rainwater harvesting system for your project.

Lesson Content

3.1 – How to Calculate Water Demand

3.2 – Measure Roof Top Surface in Google Earth

3.3 – Try it yourself

Now that you know how to measure rooftop surface in Google Earth, try it yourself here.

3.4 – Rainfall Data to Calculation Tool

3.5 – Rainwater Harvesting Calculation Tool

3.6 – Try it yourself

This calculation tool can help you to find out of rain water harvesting is cost-effective for you. If can also help you in determining the right water storage tank size. Water storage is the main costs of a rain water harvesting system. In addition it will give you an indication on how much money you should allocate.

The only climate data you need to fill out are monthly rainfall statistics which are readily available. Please note that these monthly rainfall data are averages and that daily rainfall can be very erratic.

You only need to fill out the fields in blue. In the costs sheet, the costs are provided at south-east asian price level. If you want you can adjust these figures to fit your local situation

Find out the calculation sheet here.

3.7 – Reflections on Calculation Tool