When most people think of rainwater harvesting, they picture a 55-gal tank that collects rainwater from the roof to water plants — but this term also extends to natural collection systems like dams. Rainwater harvesting is nothing new; it has been around for centuries, dating back to ancient Egyptians who used earthen dams to control runoff. Another example is the rice terraces of the Philippines, which are still in existence today. More sophisticated rainwater systems have been uncovered by archaeologists in Crete, Istanbul and throughout the Mediterranean region.
As urbanization increased, the practice of rainwater harvesting almost disappeared, except in areas where it became necessary — rain is the only source of water in certain semi-arid climates. Now, rainwater harvesting is making a comeback as drought plagues some regions of the world and managing storm water runoff is necessary in others.
Rainwater harvesting in the U.S. has gained popularity in recent years to help supplement water supplies in areas where drought conditions are affecting the water table, especially in Texas, Arizona and Southern California. Most rainwater reuse systems provide water for non-potable applications like irrigation, watering livestock, washing and flushing.
As rainwater harvesting becomes more prevalent, states and local governments are implementing regulations and restrictions upon its use. In fact, some states have strict laws prohibiting the collection of rainwater due water rights laws. States that do allow the collection and use of rainwater for potable applications include Texas, Oregon and Ohio.
In addition to conserving water, rainwater harvesting helps manage storm water runoff. In the summer of 2013, Ohio experienced record rainfalls that caused significant flooding of homes because storm water systems were not capable of handling the amount of rain that fell in a short period of time.
After my own personal experience with flooding and the rising cost of my sewer bill, I decided to examine my options. I discovered that my regional sewer district offers a credit program for those who install rainwater collection systems and take other measures, like planting a rain garden.
Other states and local districts offer similar programs, so check with your sewer department. Some states even have programs that give back a percentage of the money spent on a rainwater collection system as additional incentive. While it may seem that only a small amount of water can be collected in rain barrels, consider that, if everyone had one, it could make a big difference.
Contaminants to Consider
When collecting rainwater for drinking purposes, there are contaminants to consider. As rain falls through the sky, it can pick up contaminants that are in the air, as well as those that may be on rooftops. The first, and probably most important, contaminants to consider are microbiological, including bacteria, viruses, cysts, and parasites like Giardia and Cryptosporidium. States that allow rainwater to be used for potable applications require disinfection for bacteria and microfiltration for cyst reduction.
Water is a universal solvent, and it will try to dissolve anything with which it comes into contact, including roof material. This can be a significant source of contamination. Most roofing shingles contain some amount of asphalt material. According to NSF Intl. standards, asphalt-coated materials that may be in contact with drinking water should be tested for a variety of contaminants, including heavy metals like antimony, arsenic, barium, beryllium, cadmium, chromium, copper, lead, mercury, selenium, thallium, molybdenum, vanadium and magnesium. Additional recommended testing includes organics like volatile organic compounds or other synthetic organic compounds that would be uncovered by a gas chromatography-mass spectrometry base neutral scan. These tests would uncover contaminants that could be leached from asphalt-
The final group of contaminants that could be present in rainwater are radiologicals, specifically tritium, which is naturally produced in the upper atmosphere when cosmic rays collide with nitrogen atoms in the air. Also consider that when the Fukushima Daiichi nuclear reactor in Japan failed after the March 2011 tsunami, radioactive isotopes like cesium-137 and iodine-131 were found in rainwater in the U.S.
When considering a rainwater harvesting system that may be used for drinking water applications, it is important to consider area activities. For instance, some agricultural areas use airplanes to spray fields with pesticides. Another example is heavy industrial areas — where there are smoke stacks, and rainwater collection may not be a good option.
Rainwater harvesting is a great way to help communities manage storm water runoff to reduce flooding while providing an additional water resource. In some areas of the world, rainwater offers communities and homeowners a reliable supply of potable water. A good example is Bermuda, where all new construction must provide adequate rainwater harvesting, as it is the primary source of domestic water for residents.
In the U.S., laws pertaining to rainwater are enforced by state and local governments, so before installing a harvesting system, it is important to understand the regulations. As previously mentioned, some states do not allow rainwater collection, while other states provide incentives to collect it. As freshwater supplies become more contaminated, rainwater harvesting will begin to play a bigger role in supplying water.
Regulation & contamination factors for potable rainwater reuse applications