Is it safe to drink the water collected when it rains? Drinking rain seems so natural. Most people assume the answer is “yes.” However, other people think drinking unfiltered water is crazy. Who is correct?
We want to help you know if you can drink rain water and feel confident about what you are putting in your mouth.
What Is Rain?
If you remember middle school science, then you know about the water cycle. Here’s how it works:
- Water evaporates from the Earth’s surface. The water vapor rises into the sky.
- At higher altitudes, the water vapor cools. Cooler vapor condenses into clouds.
- The clouds ‘break’ and the condensed water falls as rain.
- Rain collects on the surface in rivers, lakes, oceans, and other spots. After a time, it evaporates again.
The hydrologic cycle is much more complicated and fascinating than you might remember. NASA’s website has a great section dedicated to explaining how water moves around the planet.
So, in short, rain is water that has evaporated, cooled, condensed, and then fallen out of the sky. Because the process begins with evaporation, the water is exceptionally pure and clean. You could just tip your head back in a thunderstorm and drink your fill. The water would be perfectly safe.
It might not stay pure, though. Let’s look at how rain might become contaminated and unsafe to drink.
How Can Rain Become Polluted?
As we mentioned, condensed water is very pure. In fact, you can make saltwater drinkable by evaporating the water, condensing it on a cold surface, and then collecting it to drink. However, rain can be polluted and unsafe. There are two primary ways this can happen.
Where the Rain Falls
Water is the universal solvent. This means it can dissolve many different compounds. Its usefulness as a solvent can cause problems for drinkers. Rain falling through polluted air can collect pollution.
Acid rain is the term for polluted rain due to industrial activity. Acid rain is safe to drink, but not pleasant. The pH of contaminated rain is commonly 4 but can be as low as 2. For reference, orange juice has a pH of 4 and lemon juice has a pH of 2.3. Both lemon and orange juice are safe to drink.
Real problems occur when more harmful pollutants are captured by the rain as it falls. These could be benzene, formaldehyde, and butadiene. Even without drinking them, people can be affected by breathing.
In summary, rainfall in highly polluted areas could be harmful to your health.
More information about rain pollution is available from the EPA.
Where the Rain Lands
The next problem occurs when the rain lands somewhere. Its collection point can be a source of dirt, contamination, and pollution. Here’s a simple example: rain falling on a field where sheep are grazing will form puddles. These will quickly be polluted by contact with sheep droppings. Such an extreme example makes a simple rule clear.
Drink it from the air, clean it from the ground.
If the rain falls directly into your mouth, then you can probably drink it without any issue. Once it lands, you should consider the cleanliness of the collection system. Here are a few ways water becomes contaminated once it lands:
- Runoff from roofs can pass through bird droppings, roofing compounds, and dirt collected in gutters. All these can make the water less safe to drink.
- Rain passing through trees can also contact animal feces, chemical contamination, and dirt. The cleanliness of the water is hard to quantify.
- Collection points such as streams, ponds, rivers, and lakes may contain any number of sources of pollution. Water from these should always be filtered and sterilized.
As you can see, drinking rainwater is safe but not necessarily easy since it must be collected. Collection can add pollution to the water.
Is it Safe to Drink Rain Water?
The short answer is “yes.” People have been drinking rainwater for thousands of years. Even with minimal cleaning, rainwater is usually safe to drink. Now that you know, let’s move on to how we can help you use this knowledge in the outdoors.
How to Harvest Rain for Drinking
There are a huge number of ways to collect rainwater. Using a few methods can really extend your water supplies during expeditions. The simplest methods are also very effective and portable.
Lightweight Water Harvesting
Let’s start with the easiest possible method: your tarp. A typical hiking tarp is 8’ x 6’ in size. If you collected ½” of rain from this surface, then you would have more than 14 gallons of water to drink. This is more than enough to satisfy your needs for a few days.
To make this work, there are some easy steps to follow:
- Stretch your tarp out somewhere exposed to the rain. Connect one side (both corners) to a ridgeline stretched between two trees.
- Use stakes and ropes to peg out the two lower corners several feet off the ground. Pull the tarp reasonably tight.
- On the lowest edge, use a peg or weight in the middle so it forms a funnel.
- Position your container below the funnel and wait for the rain!
Unless your tarp is super dirty, this method should net you some water that is ready to drink right away.
Another way to use your tarp is to keep it on the ground. Check out this video for a quick guide:
Rope Hose Collection
Our second method is even more portable than your tarp. However, it will produce less water and is slightly less reliable.
To make a rope hose, just tie a length of rope around the nearest tree. Thicker rope will work better than thin rope. The rope should pass around the tree at an angle so one side of the loop is higher than the other.
Once the loop is formed around the tree, rotate it so the loose ends are at the lower end of the loop. Hang these loose ends into your water bottle. When it rains, water will run down the tree, be stopped by your rope loop, and then trickle down the loose ends into your container.
The rope hose isn’t quite as reliable as a tarp. Trees collect their water! However, if you know you’re in for a wet night, then you can easily set this up before you go to bed. You should have a full water bottle in the morning.
Bigger Collection Systems
Some people travel and trek to fixed camps and stay out in the wilderness for weeks at a time. Rainwater collection is incredibly useful for these situations. There are some things to consider when putting one of these in place.
- Keeping the water in a container is a necessity for easier filtration and purification. Allowing it to run into a pond or natural basin will make it more difficult to pump and clean.
- If possible, use a large container that can have a tap installed several inches above the bottom. This will allow any sediments to collect in the bottom as the water settles.
- A simple screen or sponge in the input water line will catch a great deal of solid debris and dirt before the water enters the tank.
To form one of these systems, a roof can be used as the collection area. Water can be diverted into the container through gutters.
Another possibility is to use a tent as the collection surface. The water can be collected by digging a trench around the bottom of the tent. At one side of the tent, extend the trench and dig a hole to collect water. A bigger hole means more water storage. Water collected this way must be filtered and purified.
Water Filtration Basics
Making water safe to drink is relatively simple. There are only two parts of the sanitation process: filtering and purification. Each of these can be accomplished with common camping and hiking equipment.
The easiest way to filter water in the field is to use a dedicated water filter. These can be very technical or very simple. An example of the simple filter is the Millbank Sediment Filter Bag. Canvas shaped into a sock is filled with water and hung from a tree. The water passes through the canvas, runs down the toe of the sock, and is collected in a bottle.
Speaking of socks, yours make excellent water filters. Take a pair of socks and put one inside the other. Pour water in the ankle hole and collect it from the toe. Several socks together will catch most of the sediment in water. This doesn’t make the water safe to drink. Filtration removes most of the dirt and debris you don’t want in your stomach.
Once your water has been filtered, then you should purify it. Filtering removes dirt and debris from the water. Purification removes chemicals and bacteria that might make you ill. Once again, we have an easy way for you to purify your water: boil it.
Simply put, bringing water to the boil will kill all the bacteria and viruses known to make you sick. Put your filtered water in a kettle, pot, or something safe to heat, and then boil it. Once it has reached a rolling boil for a couple of minutes, it will be safe to drink (when it’s cool again!).
A bonus to boiling your water is the fire. Use the heat to dry out your socks and warm up your hands. Cook your food at the same time.
The CDC publishes more information about making water safe.
These same techniques of filtration and purification can be applied to water collected from any source. Streams, rivers, ponds, and lakes can all be good water sources.
Can you drink rain water? Yes, you can. However, you should be careful about the two things we mentioned: where it falls and where it lands. Once it has been collected, you may need to filter and purify it if it has been contaminated during the collection process. Once you master the easy techniques for harvesting rainwater, your expeditions and camps can be extended. Get out and enjoy the outdoors. Bring on the rain!