To Catch the Rain (Grafman)

Rainwater Harvesting

The basic concept of rainwater harvesting is to catch the water falling from the sky and use it with more direct purpose and before it gets dirtier from the ground. Section 1.2 covers the main types of systems, Section 2 covers the components of a rainwater harvesting system, Section 3 covers gravity and pressure, and Section 4 dives into the calculations for sizing various aspects of a rainwater harvesting system.

Section 5 describes community engagements that built the types of systems covered in this book while Section 5.7 covers some organizations implementing this knowledge. The background and history of rainwater harvesting are rich and out of the scope of this book. If you are interested in learning more, please see the resources in Section 6. Finally, Section 7 contains problem sets to test your knowledge and prepare you for designing your own unique system.

Rainwater Harvesting Types

Rainwater harvesting is a highly customizable technology. Myriad solutions exist across a global context. Rainwater harvesting systems can usually be categorized as either passive or active types. A passive type uses almost no mechanical means to capture, convey, or treat the caught rainwater. An active type uses mechanical and/or electrical means to capture, convey, and/or treat rainwater.

I often avoid using the terms passive versus active and instead refer to landscape versus built types. Landscape type systems of rainwater harvesting, as shown in Figure 1-1, use landscape features to slow, absorb, and/or store rainwater. Landscape type systems are usually considered passive.

A characteristic important to all rainwater harvesting systems is the source of pressure. Pressure is what moves water from one point to another. The source of pressure can be gravity or pumps. Gravity systems have the benefit of lower cost, lower maintenance, and being generally more robust but they rely on elevation change. Pump systems have the benefit of being able to generate the needed pressure independent of available terrain, but are higher cost and require energy input.

A final important aspect of rainwater harvesting systems is their scope and/or size. Rainwater harvesting systems can serve a small garden, a house, a school, a community, or an even larger project. The larger the scope and size, the more costs are involved and the more water can be utilized. This book focuses primarily on built, dry, gravity-fed systems for garden, household, and small organizations.

Built rainwater harvesting systems use various components to best meet needs. These components can be broken down into catchment surface, conveyance (gutters and downspouts), screens, first-flush, storage, water purification, and end-use.

1. Catchment surface – area that the rainwater falls on to be captured.
2. Conveyance (gutters and downspouts) – transports the water from catchment to storage or use.
3. Screens – separates debris from the water.
4. First-flush – diverts the first, and dirtiest, portion of rainwater.
5. Storage – holds water for later use.
6. Purification – cleans the water to the needed level.
7. End-use – gives purpose to the system!