Rainwater Harvesting: An Innovative Way to Collect Drinking Water
Rainwater harvesting is an age-old practice of collecting and using rainwater that has become more popular in recent years. Some people are trying to reduce water usage costs while others are concerned about water quality and possible contaminants in their drinking water. If you are considering rainwater harvesting read below for some useful information to help you better understand the process.
A rainwater harvesting system consists of several components:
- The catchment surface: This can be a roof or other apparatus that initially collects the rainwater. If using a roof, please note that composite or asphalt shingles are not appropriate for drinking water collection.
- Gutters or downspouts: These help to channel the water from the catchment surface.
- Leaf screens: Use screens to remove large debris like twigs and leaves from the rainwater. You may also want to use a first-flush diverter which prevents the initial flow (usually several gallons) from entering a storage unit. This device diverts water containing smaller impurities like pollen, dust, and bird feces away from the storage unit, often to a planted area for fast absorption.
- Storage tanks: Storage tanks, also referred to as cisterns, store the water for future use. The storage tanks can range from trash cans and steel drums to tanks made of fiberglass, polypropylene, stone, or even wood. The type of storage tank depends on precipitation rates, water demand, length of dry spells, catchment surface area, and other considerations.
- Delivery system: Complex rainwater harvesting systems also have a delivery system that allows the water to be gravity-fed or pumped to the location where it will be used.
According to the Colorado State University Extension website, rainwater can contain contaminants like arsenic and mercury which are absorbed from the atmosphere. The water may also contain small fecal matter, microorganisms, and other impurities that the screens and diverters do not remove. If the water is to be used for drinking, it needs to be tested and treated. One treatment solution is to use a water purifier to remove harmful biological and chemical contaminants. While the rainwater may contain harmful contaminants, it will lack minerals like calcium and magnesium which are normally found in groundwater. Since these are beneficial to have in drinking water, you may want to consider adding minerals to the water.
While you may be intimidated by the initial process of setting up the rainwater harvesting system, keep in mind that it will be worth the effort. For every square foot of catchment area, you can harvest about 0.6 gallons for every one inch of precipitation. So if you are using a 1,000 square foot roof as a catchment surface, you can expect to collect approximately 600 gallons every time it rains one inch! It is very important to understand average precipitation amounts for your area. The Western Regional Climate Center has maps that show the annual average precipitation for every state. If you are thinking about constructing a rainwater harvesting system be sure to check with state and local regulations as there may be permits or other requirements that may apply.
For more information about creating a rainwater harvesting system, the Texas Manual on Rainwater Harvesting is very useful. If you would like a professional to design and install the system, the American Rainwater Catchment Systems Association (ARCSA) offers a searchable online directory.