This article has been updated.
We had been drinking water from our rural well for about two years when we decided to have it tested. It turned out that our water had 300 times the iron recommended for human use. That sent us to our roof and the collection of rainwater for our potable water source.
Why harvest rainwater?
With increased droughts and dry spells, notably in the western states and provinces, harvesting rainwater, especially during the rainy season for use in the dry season makes sense, both personally and for our larger communities. India, Tanzania, Australia, Hawaii, British Columbia, Washington, Oregon and California have all experienced rainwater shortages in recent years. As climate change intensifies the frequency and intensity of drought worldwide, this situation is only getting worse.
According to data from US Drought Monitor, as of July 2022, more than half of US states have recorded dry periods ranging from extremely dry to exceptional drought conditions.
By reducing extraction from aquifers and rivers in dry summer months, we help ensure that there is sufficient water left to maintain critical base flow in streams
Rainwater harvesting reduces stress on local aquifers and rivers, leaving more water available for communities and environmental needs. By reducing extraction from aquifers and rivers in dry summer months, we help ensure that there is sufficient water left to maintain critical base flow in streams in order to protect fish and aquatic health. Reducing groundwater extractions can also help reduce salt water intrusion in coastal areas, as excessive pumping of wells along the coast can pull salt water from the ocean into groundwater. (3)
Research posted by the American Rainwater Catchment Systems Association (4), rainwater catchment is an increasingly popular and accepted practice in the US.
The basics, codes and licences
At a minimum collecting and storing rainwater for future use requires a catchment area, a conveyance system and a storage tank. Normally, a catchment system also includes a pump, water treatment system and fixtures. Another addition, the “first-flush diverter”, allows the first rainwater to be diverted to a container that once full, is then by-passed to the next collection unit. According to a study that measured contaminants in the first-flush container, this allows many elements that may pose a health risk to be diverted from the collection system. (5)
When designing and installing rainwater harvesting systems, it is important to consider codes, regulations and standards. Mark Miller decided to collect rainwater to wash cars sold at his Toyota dealership. He discovered that the state of Utah considered the water a commodity that he needed a license to collect. But through his desire to help the environment, he ended up winning a LEED gold award for his actions.
Here is a list and link to many state’s water collection laws:
Rainwater harvesting is permitted (and sometimes mandated) in regions of Germany, Australia and the U.S. and Canada. In the U.S. the ARCSA recently announced that the American Society of Plumbing Engineers has approved an American National Standard to assist professionals and end users in safely implementing a rainwater catchment system.
Designing rainwater collection systems
Barry Churchill has been collecting rainwater for 40 years on his off-grid home site that is not served by any utilities.
“Why let the water get into the soil and let it collect there, and then have to pump it back up? It’s all the same water.” With the exception of artesian well water, Barry has learned that water from western skies, where there is little concern about pollutants from nearby industrial areas or acid rain, is an exceptional source of both potable and nonpotable water. He created a catchment system that he now installs on other people’s homes in his rural area.
Type of roofing
He suggests that any type of potable roofing material, such as clay, tile or metal is acceptable. However, he warned me that it is not generally advisable to use the existing roof on your home if you have a wood stove because of the creosote, which would transfer contaminants to your water.
Another warning he gave me was to avoid using any kind of bleach as a disinfectant because if there is organic material diluted into the water, it will become toxic.
“Why let the water get into the soil and let it collect there, and then have to pump it back up? It’s all the same water.”
Because he uses wood heat, Barry has designed an independent collection system. His system includes a site-specific wood frame, covered with light colored metal roofing – to reduce heat buildup on the roof which can increase potential contamination. His systems are typically 24’ x 22’ with gutters at the lower end which transfer the water to pipes that then drain into a series of tanks or cisterns. From here a series of plastic pipes lead to the house and garden areas.
Collection and storage
In Barry’s coastal area, the average rainfall of 36” a year means he can collect 3400 gallons of potable water from a 22’x24’ catchment roof. Barry stores the collected water using 14, 250 gallon tanks. With a small submersible pump, or a hand pump to get it started, he has enough pressure for a shower with only one moving part.
Barry recommends that the system be designed as close to the ground as possible because it is easier to clean and has less wind resistance. He uses a minimum filtering system, employing window screens over the gutter and a cloth filter fitted to the ¾ “ waterline leading to his house.
He didn’t recommend the larger 1500 – 2000 gallon tanks in colder areas because if it freezes, you risk losing all your water. He explained that smaller tanks plumbed together make it more manageable, especially if you lose water from one tank, you’ve still got another to draw from.
Don’t forget the slope
Barry built his system ensuring that he had 8’ of head above the level of his kitchen sink. He said as long as the bottom of the tank is above the counter top you have pressure. If it’s only something like 2’ there is less pressure. He recommended a gentle slope to the roof collection system, “so the rain has less chance to run off over the gutter.” He cleans his catchment roof once a year.
Homeowners who do not have the space or are not prepared to build a system like the ones described above, can start with a simpler system using rain barrels which store water collected from the downspout. These simple systems are primarily used for non-potable water applications such as landscape watering. Most rain barrels can also be connected in series for additional storage capacity. These systems can also be moved easily if the owner moves to a new residence.
A study of various roofing materials
Ensuring your water is not contaminated is essential. A study by the Texas Water Development Board showed test results from five different roofing systems that were measured for contaminants. The five roof types were shingle, Galvalume® (a type of metal roofing), tile, cool, and a green roof, which were all compared to ambient rain. (5)
Water was collected from several rain events using a first-flush diverter and then stored in two connected tanks. The water was analyzed for the following: pH, conductivity, turbidity, total suspended solids (TSS), total coliform (TC), fecal coliform (FC), nitrate, nitrite, dissolved organic carbon (DOC), and selected metals.
An important finding (first mentioned by Barry) which was confirmed in the Texas study concluded that rainwater that has DOC (organic matter dissolved in water) should not be treated with chlorine, because this creates disinfectant by-products known to be harmful to human health. In the Texas study, they recommended that green roofs and asphalt fiberglass shingle roofs not be disinfected with chlorine for this reason.
Before you jump to the conclusion that green roofs are just not viable for rainwater harvesting, there is another interesting finding in this study. Coliform counts from the green roof were lower than the other five roof types tested. However, the green roofs contained the highest concentrations of arsenic and lead. So if you are considering collecting rainwater from a green roof, you would need to test the water after installing the water collection system to determine what type of filters would take out these heavy metals.
Our work shows that harvested rainwater quality generally improves with roof flushing, indicating the importance of an effective first-flush diverter. However, the rainwater harvested after the first-flush from all of the pilot-scale roofs did contain some contaminants at levels above United States Environmental Protection Agency (USEPA) drinking water standards (i.e., turbidity, TC, FC, iron1, and aluminum); the harvested rainwater after the first-flush from the full-scale Kynar®-coated Galvalume® roof exceeded the turbidity, TC, and FC standards. (5)
Although the Kynar®-coated Galvalume® metal roofs are the recommended choice by most contractors, this study concluded that concrete, tile and cool roofs are also good candidates. (Cool roofs effectively reflect the sun’s energy from the roof surface and emit infrared heat.) Based on all their specific tests, and acknowledging the time and location of the study, the authors recommended that harvested rainwater be disinfected prior to potable use.
Sylvain, another rainwater harvesting contractor I spoke with, said he would use a normal house roof if it didn’t have a wood stove. Otherwise, he designs systems that site the roof directly over the cistern. He prefers to use the Galvalume® metal roofing material, which he considers the safest choice.
I asked him about his preferred filtration system. He adds two screens if the water is non-potable, but if is potable he uses four filtration systems. The first is a screen filter on the tank, and the second a prefilter. He then uses ceramic disk filters which are specifically designed to remove pathogenic bacteria, cysts, and chemical and heavy metals.
Importance of water testing
If you decide to collect rainwater for potable uses, my conclusion after talking to these two contractors and researching the topic is to install the system using the roofing material of your choice, including the first flush diverter, cisterns and piping and then have the water tested. Then you will be able to determine the best filtration or treatment systems to use for your specific system and area.
Harvesting rainwater is a great idea if you live in an area that experiences water shortages, if you are concerned about the water coming from your existing well or community supply, and if you live in an area far from industrial pollutants.
Areas with the Highest Normalized Deficit Cumulated (NDC) index. This index pulls from more than 60 years of precipitation data and the current water use pattern for the United States in order to better depict the discrepancy between water use and availability.
- Washington DC metro area
- New York metro area
- California area, from San Diego to Santa Barbara and inland
- Agricultural belt: Dakotas
- Agricultural belt: Nebraska
- Lower Mississippi belt: Arkansas area
- Agricultural belt: North Texas
- Agricultural regions in Ohio
- Agricultural regions in Minnesota
1 The U.S. Drought Monitor is produced in partnership between the National Drought Mitigation Center at the University of Nebraska-Lincoln, the United States Department of Agriculture, and the National Oceanic and Atmospheric Administration.
4 ARCSA website (arcsa.org) also has resources such as lists of US laws, rules and codes, rainwater harvesting manuals, technical guidelines, economic and practical studies and links to average precipitation maps, information on green roofs, presentations and webinars on the technological aspects, and much more.
5 Effect of Roof Material on Water Quality for Rainwater Harvesting Systems – Additional Physical, Chemical, and Microbiological Data, Texas Water Development Board, Austin, Texas, January 2011.