One of the principles of rainwater management is to slow the water by collecting and using it onsite and slowly infiltrating any excess overflow. Collected rainwater can be an important source of high-quality water for crops, greenhouses, livestock and humans even in very arid climates.

Rainwater harvesting has been used for thousands of years. The Old Testament mentions cisterns at least ten times, and rainwater harvesting systems in the Middle East date to 5,000 years ago. In the U.S., water shortages, quality concerns and stormwater mitigation have renewed interest in this ancient practice.

The most enlightened rainwater harvesting practices involve a recognition and exploitation of the relationships among the four components of ARCSA’s mission: potable, nonpotable, stormwater and energy. For example, sustainable harvesting of rainwater for gravity-fed nonpotable drip irrigation diminishes the stormwater impact of rain events, decreases the water-energy footprint and displaces the need for an equal amount of highly treated potable utility water.

Rainwater can be used for any potable or non-potable use.

There are many reasons to harvest rainwater: quality of the resource; reduced appliance maintenance due to low mineral content; availability of a secure, onsite water source; and greater nutritional value for crops and gardens. Some successful rainwater harvesting businesses are growing because they make Return on Investment arguments to potential clients. Their rationale is based on the current and growing cost of utility water, the value of a rainwater harvesting system relative to other potential investments, the ability to mitigate costly stormwater effects, the quality of rainwater relative to utility water, the relative security of distributed water systems and — for a select few — the altruistic benefits.

Increasingly, consumers are attracted to rainwater for the quality of the resource. While surface and ground waters suffer from contact with the contaminants that are plentiful in those water sources, rainwater has fewer contaminants to deal with, and those can be reduced or eliminated by discarding the first portion of each rain event by using a “first divert” system, and by using the components and materials approved by the National Sanitation Foundation for rainwater collection. As a testament to the quality of rainwater, ARCSA endorsed six rainwater entries in the prestigious Berkeley Springs [West Virginia] International Water Tasting competition held in February, 2011. Rainwater from Texas-based SparkleTap won First Prize in the Purified Water category, and Virginia-based RMS took fifth place.

Rainwater harvesters are first conservation and efficiency advocates. It makes no sense to spend precious funds to augment water supplies if one has not first extracted the greatest benefit from water efficiency and conservation opportunities.
In a related sustainability field, the same is true of exhausting energy efficiency and conservation opportunities before installing a photovoltaic system. If one was driving down the road and found that one’s parking brake was on, the first solution would be to release the parking brake, not to add more power by buying a bigger engine. Thus if one has not implemented water conservation and efficiency opportunities, it is premature to harvest rainwater.

A recent survey of the US rainwater harvesting market reveals substantial growth in the face of an otherwise stagnant economy. While it may appear that harvesting rainwater is simple, the best rainwater harvesters are multi-disciplined professionals. We strongly recommend that aspiring rainwater harvesters join ARCSA, avail themselves of one of ARCSA’s periodic rainwater harvesting workshops.

The impact of climate change will vary greatly from region to region, but most studies agree that climate change will result in more intense storms, and these storms would result in more water runoff. Rainwater harvesting allows us to capture this runoff, put it to a useful purpose and slowly infiltrate overflow.

The major components of a rainwater harvesting system are the collection surface, gutters, downspouts, pre-filtration systems or first-flush devices, storage tanks and distribution systems — which can include sanitization.

Modern tanks used for residential and commercial applications are available in all sizes and can exceed one million gallons. The Romans built huge cisterns under Istanbul; the largest stored 80,000 cubic meters (21 million gallons).

Rainwater must be treated to be safe to drink. The U.S. Environmental Protection Agency publishes drinking water standards that define the maximum contamination level for potable water in the U.S., and while they apply only to public water supplies serving more than 25 people, it is prudent to apply the same requirement to smaller systems.

One of the most frequent drivers for rainwater harvesting is compliance with the EPA’s and states’ stormwater rules. Well-designed rainwater harvesting systems will make full onsite use of the rainwater, in most cases slowing it down until it is infiltrated on property, so it does not become problematic stormwater.

There is a growing awareness in the U.S. that rainwater harvesting is at least a partial solution for potable, nonpotable, stormwater and energy challenges. National, state and local jurisdictions are developing legislation, codes and ordinances that encourage the practice.

ARCSA Design and Installation Standards have been incorporated into the IAPMO Green Plumbing & Mechanical Code Supplement of the Uniform Plumbing Code (UPC), and the International Green Construction Code of the International Plumbing Code (IPC). States will refer to their reference plumbing code (either the IPC or UPC) and can be expected to incorporate these new standards over the next three years.