rain flows down from a roof down

Why You Shouldn’t Drink Rainwater

Rainwater harvesting can bolster your water supply for washing, bathing, gardening, and more. But is that rainwater safe to drink?

In many cases, you can get by drinking rainwater without adverse effects. However, as rain falls through the sky and runs off roofs, through gutters, or across the ground, it can be tainted by some pretty nasty contaminants. Compared to filtered water, rainwater is riskier to drink. Read on to find out everything you need to know about the potential dangers of drinking rainwater and how it stacks up to filtered water.

Isn’t Rainwater Harvesting Illegal?

In many places, there are strict regulations surrounding drinking water. The United States, for example, has laws on the book that make the distribution of rainwater for drinking purposes illegal if the collected rainwater isn’t filtered and treated first. 

That being said, the act of collecting rainwater itself isn’t typically illegal unless it infringes upon someone else’s water rights. Specific rules surrounding the collection of rainwater vary greatly from place to place. In some places like Australia, rainwater collection is not only not illegal but encouraged and sometimes required.

A glass of contaminated water on a table.

Rainwater may reasonably be expected to contain at least small amounts of some contaminants.

Potential Dangers of Drinking Rainwater

According to the Centers for Disease Control and Prevention (CDC), rainwater can carry contaminants that may make humans ill. Here are a few of the most common contaminants that may leach into rainwater as it falls through the air or over common building materials like shingles and gutters. 

1. Bacteria

Particularly during the earliest part of a rainstorm, high levels of bacteria are present in rainwater. One of the most common bacteria is E. coli, which may cause gastrointestinal inflammation and diseases such as meningitis or Crohn’s disease. Salmonella, shigella, campylobacter, vibrio, and pseudomonas are also possible contaminants in rainwater. While filtration and water treatment reduce the risk of illness from these pathogens, avoiding rainwater consumption altogether is the safest choice.

2. Parasites

Giardia is one of many parasites that can be picked up in rainwater and delivered into the human body via consumption. The parasite causes giardiasis, a disease that affects the uptake of nutrients in the lower intestine and reduces digestive efficiency. 

Other parasitic microorganisms that can be picked up in rainwater include cryptosporidium, which causes both gastrointestinal and respiratory problems. Rarer parasites like naegleria fowleri, or the “brain-eating amoeba,” have been found in warm freshwater sources and could make it into collected rainwater depending on the circumstances. 

3. Toxic Chemicals

Runoff collected near agricultural areas and chemical plants or in personal yards that have been treated with fertilizers or pesticides is unlikely to be fit for human consumption. While reverse osmosis water filtration systems can remove nearly all chemical contaminants when used properly, the only surefire way to prevent the ingestion of harmful industrial chemicals is to avoid drinking rainwater.

Besides gardening and farming contaminants, pollution from cars and factories can also contaminate rainwater and limit its drinkability. Smog, smoke, and dirt with all kinds of harmful contents can easily be picked up as rain falls to the ground and drains.

4. Heavy Metals

Rainwater can dissolve heavy metals like lead and zinc from air pollution, roofing materials, or sections of the catchment. People who collect rainwater for drinking and other household uses must take care to build a rainwater collection system out of food-grade materials and keep the system clean at all times to prevent contamination from heavy metal pollutants.

Rain barrels or rainwater tanks can leach harmful contaminants over time. If groundwater can leak into your system, the likelihood of having clean water for drinking or other purposes is very slim. Asbestos and asphalt can also find their way into stored rainwater.

Building a Safe Rainwater Harvesting System

Constructing a system for collecting runoff and rainwater that’s suitable for human consumption takes lots of hard work and upkeep. Choosing the right materials for the roof, the water storage receptacle, and the entire pathway of the running rainwater can be challenging. Sometimes the materials themselves slowly leach chemicals into the drinking water over time. 

Keeping the whole system clean also takes great effort. Protecting the collected water from animals and unclean runoff takes nearly constant maintenance. Screens and other devices are used to keep large animals and sediment out of the water. But even if you do protect your collected rainwater, it should be used within 10 days of collection so that mosquitoes don’t lay larvae inside it. 

With all of these considerations, building a safe rainwater harvesting system that’s completely clean of contaminants can be incredibly difficult. It’s not always feasible or worth the hassle, which is why the majority of homeowners prefer to stick with public water sources rather than construct an entire rainwater harvesting system.

Rainwater Purification

Can you create safe drinking water from the rain with proper treatment? Depending on the starting quality of rainwater, it may be possible to make the water safe for consumption. The trouble is that some of the contaminants may make it through the filtration system you have in place. If you drink rainwater without filtering it properly, you’re putting yourself at unnecessary risk. 

Treating collected rainwater certainly reduces the number of contaminants. However, each time new water enters the water harvesting system, you have to retreat the water. With a filtration system, the process is a bit easier because it will be automated, but the upkeep of a more complicated system is more involved. 

Drinking Rainwater Vs. Tap Water

Municipalities often add elements like fluoride to the public water supply. This additional fluoride helps protect against tooth decay. Even if the country or municipality doesn’t practice fluoridation, sodas and bottled water may sometimes have fluoride content. The additional fluoride in the public water supply is a divisive issue. While approximately 70% of Americans have fluoridated water, entire countries such as Belgium and Denmark don’t add fluoride to their tap water at all. 

Tap water may also have trace elements of aluminum, ammonia, arsenic, copper, chromium, mercury, and nitrates, among other things. That may sound like a frightening laundry list of harmful contaminants, but with the right water filter, tap water is much less risky than filtered rainwater. 

Environmental Concerns

In some scenarios, rainwater collection on a personal level isn’t enough to interrupt the supply for creeks and other bodies of water. Catching rainwater is a great way to increase a personal water supply while avoiding single-use plastic water bottles.  In especially rural places where public water systems aren’t in place, collecting rainwater and treating it with a disinfection agent might be the best way to get a large amount of water for gardening or washing purposes. 

However, if you live close to cities or industrial areas, pollutants and acid rain may not come out of your collected rainwater so easily. When these contaminants have a heavy presence, rainwater may not even be suitable for watering plants or washing laundry. Testing for these environmental elements isn’t always practical or cost-effective. Home testing kits are available, but regular testing could get costly. Skipping a test could expose you to harmful elements in the water. 

Environmental concerns are only of the main motivators for many people who use water harvesting systems to bolster their home water supply. The simple fact is that letting the rain go or redirecting it without collecting it in rain barrels won’t hurt the environment but consuming dirty drinking water could be ruinous to your health. The best option where it’s possible is to rely on the municipal public water supply and treat that with the right water filter or filtration system.

For gardening or lawn care, rainwater may be fine as a backup source if you collect it when it rains and do your watering about a week later. In that case, you should still be treating the rainwater before use, especially if you’re watering fruits or vegetables that are intended for later consumption. 

Can I Use Rainwater for Washing?

If the risk of drinking rainwater isn’t worth it, could you still do other household chores like washing with collected rainwater? Some diseases are spread through cuts or soft mucus membranes like the eyes and groin, which means if you use contaminated rainwater for bathing, laundry, or washing dishes, you could still get sick. 

One such disease is called leptospirosis. It’s caused by bacteria in the urine of mammals like pigs, horses, cattle, rodents, dogs, and other wild animals. The bacteria can last in the ground for weeks or longer. Runoff can carry it right into your rainwater supply and make the whole collection unsuitable for home use, including for washing. 

What About Watering Plants?

Gardening is one area where you can use collected rainwater. That rain is going to land on the plants and grass anyway, so you may as well store some to water your garden for little to no cost during dry spells. Watering vegetable gardens is a slightly different scenario.

Theoretically, bacteria and other contaminants in rainwater could stay on the plants and make you sick once you eat them. However, since most home gardeners tend to wash their plants vigorously before cooking or eating them, you might be fine watering plants with rainwater. Of course, the final washing should take place with filtered tap water and not rainwater.

Rainwater harvesting during Monsoon season

Rainwater harvesting is collecting rainwater that falls on a structure or other impervious surface (a roof, for example) in order to store it for later use.

Alternatives to Rainwater Collection

If you’re looking for clean drinking water, the best thing you can do is get the right filter for your tap water. However, there are some other methods you can use to source water for gardening or washing. 

1. Digging Wells

If you’re lucky enough to have a well on your land or live near a public one, they can be a great source of drinking water and all-purpose water. With a portable water filter, the few contaminants in relatively clean well water are perfectly drinkable.  The CDC says well owners are solely responsible for maintaining their wells and testing the water for potability.

Common pollutants in wells include E. coli and other coliforms, nitrates from fertilizers, lead, arsenic, radium, mercury, and atrazine among others. You should also test your well water for pH when you test for these possible contaminants. The pH for groundwater should be somewhere between 6.5 and 8.5. Any higher and it could be contaminated with pollutants or chemicals that leach in through the ground. 

Protecting the well is key to make sure outside contaminants don’t enter. Animals could fall in or leave behind traces of harmful bacteria. Covering the well properly is paramount if you want to draw drinking water from it, as is using the right well water filter.

The good news about wells is that they generally stay clean if you protect them well enough and there aren’t any underground sources of contaminants that can leach in. Drinking the water may require additional filtration inside, but you can water plants and even do some washing with well water if it’s clean on a test.

2. Under-Sink Filters

You can drink tap water once it’s been filtered with the right under-sink filter. It’s the fastest way to get the cleanest possible water for drinking, dishes, watering plants, cooking, or just about anything else. It’s also far less of a hassle than building an entire rainwater collection system and maintaining it. Many under-sink water filters only need to be changed once or twice a year, which means you can install them and get clean drinking water worry-free for a much longer time.

You also don’t have to depend on the weather to bring you your water supply. If you live in a cold climate, an under-sink filter is also much better for the winter months when frozen rain or snow falls and can’t be collected or filtered as readily. 0.1-micron filters and multiple filtration stages make common under-sink filters super-effective at removing all the contaminants from drinking water and leaving behind crystal clear water that will quench your thirst and keep you hydrated.

The EPA and NSF certify some models of under-sink filters so you can trust that they’ll get rid of contaminants or at a minimum reduce their presence well beneath the threshold at which they pose a risk of illness. Certain models also remove heavy metals, which can make the tap water from just about any jurisdiction much tastier and better for you.

3. Greywater

Water from domestic sources can be captured as greywater and used for certain applications such as irrigation or exterior washing. However, water from the kitchen shouldn’t be used because it has many contaminants from food waste that soil organisms cannot break down. Understanding what is in your greywater is important for protecting the efficacy of your soil. 

If you aren’t careful and let your greywater runoff flow into local streams or someone else’s property and it causes some damage, you could be liable. It’s imperative to put a buffer zone between your property lines and anything that could be damaged by the greywater. Collecting greywater may also require a system to catch it before it goes down the drain. You can set up a drain system that leaves the greywater in buckets, just make sure you use it within about 24 hours. 

Coarse filtration can help make greywater safer for gardening or manual flushing purposes. But you should never try to clean the greywater enough to drink it. Filtering it thoroughly enough for it to turn into clean drinking water is better left to the professionals at the municipal level. 

Make sure to check local regulations surrounding the collection and use of greywater, as not all areas treat the idea the same. Generally speaking, it will be more rural places that allow for some greywater use while urban centers will frown upon the idea.

Can Rainwater Collection Save You Money?

Whether your main goal is to bolster your water supply or be more environmentally friendly, the cost of your water system is going to have a significant impact on how realistic its implementation will be. With some clever DIY, you can probably find the proper tools for a water collection system for a fairly low cost.

Other hidden costs like your labor time and the constant attention required to test and filter your rainwater to make sure you don’t get sick might make the whole rainwater collection idea a non-starter. Most people who find rainwater harvesting to be an inexpensive alternative have ideal conditions or skip some maintenance or testing steps, putting themselves at an unneeded risk for illness. 

The best way to save money and get the cleanest possible drinking water is to buy a household water filter. They need much less attention and eliminate the risk of waterborne illness even more than the treatment tap water already gets. 

Conclusion:

Many people find the idea of rainwater harvesting appealing for environmental and self-sustaining reasons. However, pollutants and contaminants can easily get into collected rainwater and cause pretty nasty illnesses in the people who drink it. Setting up the system and checking it for efficiency is a much bigger task than it might seem at first.

The best way to get clean water for all your household needs is to install a home water filtration system that will turn standard tap water into spring-fresh, completely clean water.

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Joshua Perkins

Joshua spent ten years as a water systems technician in California before settling down with his wife and two young children in Nashville in 2018. Through all of his experience, he learned the benefits and shortfalls of so many different types of water filtration systems, from pitchers to whole-house installations. He started Water Filter Authority in 2019 to empower other families to make the right decision for their long-term health and wellness.