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.