# 1: Introduction

If water is life, rainwater is a fountain of life. Rainwater is renewal. Each trip around the hydrological cycle brings a fresh start, clean water, and a new chance for health and life. Catching the rain allows us to store clean water and thrive as communities. To catch the rain is to believe in the future.

The purpose of this book is to share inspiring stories and empowering knowledge about how various communities have caught that fountain of life using rainwater harvesting systems. This book looks at real, practical, global experiences of rainwater harvesting (aka rainwater catchment) at individual and community-based levels through academic, mathematical and practical perspectives. This book can be used to learn practical skills, hear real stories, and make math have more meaning.

This book is for practitioners, DIYers, and community members looking for water solutions, as well as for students and teachers in environmental science, environmental studies, sustainable design, international development, engineering, and mathematics. There are sections on rainwater harvesting in general, types, components, gravity, calculations, stories, useful links, conversions, and problem-sets. If you are looking for inspiration, jump to the stories.

The calculations in this book are intended to take a rather general approach. Rules of thumb, as well as deeper calculations, are used. These calculations can be applied both to unique rainwater harvesting applications as well as systems beyond rainwater. The questions at the back of the book are designed for a wide range of classes. When I travel and lecture on rainwater harvesting, I always start with the same question: “Who owns the rain?” That question has no single answer and often yields creative, sometimes stunningly accurate responses, such as nature, everyone, no one, the animals, Bechtel, the people, the city, the government, Nestle, whoever used it first, the river, and more.

The next question I ask is, “Why catch rainwater?” My assumption is that if you are reading this book, you already have an idea of why. That said, here are a few reasons:

• Water security and resilience
• Less impact on the wastewater treatment plant
• Water quality
• Fewer chemicals
• Cost
• More connection to resources
• Independence
• Less energy
• Less impact on often failing sewer systems
• Less runoff, less erosion
• Less processing
• Local groundwater recharge
• Because it works
• Less waste

In some communities, the reasons are glaringly apparent – people, mostly children, are dying from preventable waterborne illness. In other communities, the reasons are more personal – deep and personal care for the environment, and/or artistic, aesthetic, or whimsical motivations. Often when people learn of the energy and chemical processes embedded in delivered water, seeing rainwater go unused invokes a greater sense of waste. For some families, it is a desire to connect their family to their natural resources and consumption. In all these cases, catching rain builds local and personal capacity and agency to build a more secure future together. The next sections lead you through how to do it and share personal stories of how it has been done.

• 1.1: 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.
• 1.2: 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.