Rainwater harvesting is a viable method of saving money on your water bill while simultaneously helping the environment. While most homeowners opt to use rainwater for outdoor applications, such as washing cars and watering plants, others might wish to pipe this water inside their homes. However, transporting rainwater indoors raises many concerns regarding the safety of using rainwater for drinking, cooking, and other indoor applications. In this article, you can find information about rainwater harvesting, how to filter rainwater to make it safe to drink, and answers to other common rainwater questions.
Why collect rainwater?
Collecting rainwater, also known as rainwater harvesting, is an excellent way to save water at home. Rainwater harvesting is the process of collecting rainwater that is typically used for outdoor applications. As rainwater runs down a roof, it collects in the gutters, runs through any number of filters in the downspouts and gutters, and flows to a water storage tank. A hose can then be attached to the tank to provide water for gardening, washing cars, watering a lawn, and other outdoor uses. Another option for rainwater harvesters is piping the collected rainwater into a home’s plumbing system. No matter what the harvested rainwater is used for, it can save you money on your water bill, prevent soil erosion, and help the environment by not filtering water for applications that do not require filtration.
Learn more: Rainwater harvesting 101 | 5 advantages and disadvantages of rainwater harvesting
Can I drink rainwater?
Without first passing through a robust filtration system, rainwater is not safe to drink. When rainwater flows from your rooftop to gutters, it can pick up contaminants such as viruses, bacteria, bird droppings, leaves, twigs, insects, and more. Even if the water fell into your tank straight from the sky, the pollution in the air would contaminate the water enough to require filtration before drinking. This contamination is more severe the more industrial the area you live in. Consuming untreated rainwater can lead to short-term or long-term health effects if consumed regularly.
Recently, rainwater was found to contain levels of PFAS, known as “forever chemicals” because of their longevity in the human body. These chemicals are linked to cancer, increased cholesterol levels, liver and kidney damage, immune system deficiencies, and thyroid problems. PFAS chemicals have been found in rainwater all around the globe, making rainwater unsafe to drink anywhere in the world.
Learn more: How to remove PFAS from water
How to purify rainwater for drinking
Two steps are required to make rainwater drinkable: disinfection and filtration. In the case of distillation, these two processes can be achieved at the same time. However, other techniques require these individual stages to be performed by different systems.
Despite rainwater being essentially distilled by the sun, gases in the atmosphere contaminate the water while it falls to the earth. Water collects dust, smoke, and air particles while it falls to your rooftop, where it can collect contaminants such as lead, copper, asbestos, sediment, dirt, bacteria, viruses, and more. Before this water can be drunk, it must be purified of these impurities. The best filtration options for making rainwater potable are reverse osmosis and distillation.
Mechanical filtration (via a sediment filter or Rusco spin-down system) is also integral to the success of rainwater treatment. A rainwater collection system can catch most large particulate matter like leaves and twigs. The most common debris found in stored rainwater is fine grains of sand and dirt. While filtration systems are equipped to remove this, you do not want to overload your RO system’s pre-filters with heavy sediment. They are designed to eliminate much smaller sediment and debris. Standard string wound or spun polypropylene sediment filters are cheap and highly effective and prolong the life of your more expensive RO filters.
Distillation
As stated above, distillation can achieve both the “filtration” and "disinfection" stages for purifying rainwater in one phase, but it does so slowly and in limited batches. Because microorganisms do not evaporate, the water that turns to vapor becomes free of these bacteria and viruses. Rather than deactivating these microorganisms like UV water purifiers, distillers physically separate the treated water from the source. Both UV purification and distillation require a degree of rainwater pre-treatment before use. You want to avoid your filtration systems from being overloaded with sediment build-up. Sediment filters are cheap, easy to replace, and efficiently eliminate particulate matter from rainwater.
Distillation is effective at separating harmful elements, bacteria, and viruses from water. This makes it a one-step process for making rainwater potable. Water distillers are not filters in the traditional sense. Rather, they heat water past its boiling point, collect the water vapor on the distiller’s ceiling, and cool down the steam to a liquid form. The resulting water is free from virtually all impurities, including contaminants treated by reverse osmosis and bacteria and viruses deactivated by UV purification.
Advantages of distillation for treating rainwater
- Simple installation
- Removes practically all contaminants
- Separates microorganisms from the final product
Disadvantages of distillation for treating rainwater
- Uses more power
- Treats water very slowly (about 1 gallon every 4 hours)
Learn more: What is distilled water and is it safe to drink? | How to remove bacteria from drinking water
UV disinfection
UV disinfection is an essential stage of rainwater purification that typically occurs as the final step of treatment. UV purifiers subject light to waves of ultraviolet light that penetrate microorganisms’ cell walls to prevent them from reproducing. This renders bacteria and viruses in the water harmless for consumption. For UV disinfection to be effective, the water being disinfected must be clear of other contaminants. For a UV system to properly operate, a sediment filter with at least a 5-micron rating should be installed before the filter to eliminate any dirt or debris from shielding bacteria or viruses. If water is not pre-treated, the contaminants will prevent the UV light from penetrating the cell walls and will not make the water safe to drink.
Advantages of UV disinfection for treating rainwater
- Uses less power
- Much faster disinfection time
Disadvantages of UV disinfection for treating rainwater
- Does not remove other contaminants from water
- Does not physically remove bacteria and viruses from water
Learn more: What is a UV water purifier and how does it work? | How to maintain a UV system
Reverse osmosis
Reverse osmosis (RO) systems are regarded as one of the best filtration methods available to households. This is in large part because of their effectiveness at removing almost all impurities from water. These impurities include sediment, salt, VOCs, lead, copper, fluoride, chlorine, and many more. However, because rainwater can contain bacteria and viruses, a reverse osmosis system alone will not make rainwater safe to drink. It must be paired with a UV water purifier to ensure that both harmful elements are removed and bacteria and viruses are killed.
Advantages of reverse osmosis for treating rainwater
- Much faster yield time
- Less energy used per unit of water
- Can be used for more applications
- Capable of remineralization
Disadvantages of reverse osmosis for treating rainwater
- More expensive and complicated installation
- Reliant on water pressure
- Requires filter replacements
Learn more: What is a reverse osmosis system and how does it work? | What is a sediment filter and how does it work?
What are the benefits of drinking rainwater?
Rainwater must be treated prior to drinking, making filtered rainwater no different than city-treated or well water that runs through your home’s filters. Drinking rainwater without filtration is not only unbeneficial, but it can be hazardous to your health. Elements such as lead, copper, and sulfur, can be acquired by rain as it flows to a storage tank. Even more harmful microorganisms such as Salmonella, Legionella pneumophilia, and Pseudomonas aeruginosa have been frequently found in rainwater. This contamination makes treating rainwater before it enters your home essential.
The only benefit of drinking rainwater over city-treated water is the money saved on your water bill. However, a very small percentage of water used in a home is consumed. As a result, drinking filtered rainwater will not have much effect on your water costs. To help save the most money, rainwater is better used for outdoor applications where it is used at high volumes.
How to filter rainwater for plants
Plants can greatly benefit from rainwater because it lacks the bacteria-killing chemicals chlorine and chloramine. You do not need the same intensive filters for plant water that you do for drinking water, but adding filters before your water storage tank will prevent large debris from making your water murky. These filters could include gutter guards, downspout filters, or mesh filters at the entrance of your storage tank. For edible plants, ensure that unfiltered rainwater does not contact the edible parts of the plant, as there is a small risk of e. coli from rooftop runoff that picks up animal feces. Maintaining a regular cleaning schedule of your water storage tank will keep your water at optimal clarity for your plants.
How to purify rainwater for bathing
Rainwater lacks hardness minerals that are hard on your skin and hair. This makes rainwater ideal for bathing, but what filtration is necessary to make rainwater safe to take a bath or shower with? Rainwater is considered safe for bathing, but consuming the water while taking a bath or shower could introduce harmful bacteria to your body. Because of this, adding a UV lamp between your storage tank and shower or bathtub is recommended. A reverse osmosis system is not necessary for these purposes because the contaminants it removes do not absorb easily into the skin.
Does boiling rainwater make it safe to drink?
No, while boiling rainwater kills microorganisms in water, chemicals, dust particles, and elemental contaminants would not be eliminated. Because water is lost in the form of steam during the boiling process, these contaminants would become more concentrated than before the water was boiled. This is why it is important to pass your rainwater through a mechanical filtration method, like a sediment filter, before treating it further.
If you have any additional questions, please do not hesitate to contact us.