Estimated reading time: 10 minutes
Every drop of water you’ve ever drunk, swam in, bathed in, or watered your plants with was once a drop of rain falling from a cloud. Of course, those drops of water were probably purified at your local water treatment plant.
But what if the treatment plant shuts down due to a major disaster? Is it safe to harvest rainwater and drink it? The answer is yes, but you have to do it right.
Instead of placing a thousand cups out in a rainstorm, you should build your very own rainwater harvesting system. This system collects rain and stores it safely for you to drink at your convenience. For sustainability and economic purposes, harvesting rainwater is an ability any long-term prepper should have.
However, there are more considerations than you might expect. Here is everything you need to know about harvesting potable rainwater.
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Step 1. Determine if Collecting Rainwater is For You
Most people don’t realize that naturally collected rainwater is not as pure as it looks. Sure, it falls from the sky into whatever contraption you use to collect it, but contaminants and germs are collected as well. This is especially true if the water is pouring off of some other surface before filling up your container. Roofs have many things sitting on their surfaces that are not safe to drink, such as animal fecal matter.
You must also be aware that some roofs may have traces of chemicals or other poisonous substances such as asbestos on them, so any water collected from the roof is most likely contaminated.
And if you live in a highly-populated area, or even near one, your rainwater may become contaminated before it has the opportunity to hit any surface. This is due to the pollution in the air. In some cases, environmental pollutants can be dissolved into the rainwater as it’s falling. So as you can see, there are many ways for naturally collected rainwater to become contaminated, and it surely will be unless preventative measures are taken.
Although treating water with iodine can be safely done when you’re camping, it is not the best treatment for rainwater. Iodine does not treat or make your collected rainwater safe for consumption if the water has been contaminated with chemicals. You will also want to make sure your collected water doesn’t remain standing long enough for mosquitos to turn it into a breeding ground.
All this is why I recommend you use collected rainwater for purposes other than consumption, such as watering your garden or flushing your toilet. I also don’t recommend rainwater if you’re ill or have a weak immune system. If your main purpose for collecting rainwater is to drink it, then you should either boil it first or use a good water filtration system (more information on that in step 5).
Step 2. Research Local Laws
The laws and regulations regarding the collection of rainwater vary from state to state, with some being stricter than others. Before you begin making plans to collect rainwater, you should first check your local laws. States such as Texas, Rhode Island, and Virginia are friendly to the idea of locals collecting rainwater and even offer tax exemptions for those who purchase equipment.
Other states will allow the collection of rainwater under strict conditions. If you would like to know where your state stands on the collection of rainwater, go to ncsl.org.
Step 3. Calculate Your Water Requirements
Once you’ve decided harvesting rainwater is for you and you’ve checked the local laws, you’ll need to figure out how much water you and your family will need. There are a number of factors to consider, and a few methods to choose from. First, become familiar with the local average rainfall charts. You’ll need to know both the total average rainfall and the months which receive the most and least rain.
Mother Earth News suggests rainwater harvesting becomes feasible with around 24 inches of annual rainfall, which brings up your first consideration. Determine how you will use rainwater:
Are you hoping to completely sustain yourself on rainwater? Are you wanting to irrigate and supply water for homestead animals as well? Or are you merely providing a supplemental supply in case of emergencies? Your answers will determine how much water storage you’ll need.
Once you’ve determined your water needs, you can use a quarterly drought system as a rough estimate for how much you need to store. If your area goes for as long as 3 months much without rain (as many summertime locales do), you will need a supply of water for that entire quarter. Calculate how much water you and your family use on a month-to-month basis and build your rainwater storage accordingly.
It may sound difficult to get a water usage estimate, but all it takes is a little time and planning. Use a tank you already have, or measure out gallons of water for everything, to see how much water you use. Then simply multiply your monthly water usage by 3 for your quarterly drought contingency to see what kind of storage system you will need.
Keep in mind that most people in the modern world use a lot more water than they actually need. People waste thousands of gallons of water for no good reason, but you won’t want to be one of those people if you harvest your own water. Not to say that you have to limit baths to once a week, but you will need to conserve more than you would if you were hooked up to the city’s water supply.
Step 4. Learn How a Water Harvester Works
The principles of a rainwater harvester are fairly simple. Rain falls onto some sort of roof, which guides the water into a storage container. However, doing so in an efficient and sanitary way takes a little ingenuity. You will need 7 basic components to harvest rainwater:
- Catchment Surface – The catchment surface refers to the roof which will collect rainwater. Generally, the bigger the better, as more square footage will allow you to store more rainwater. The catchment surface is one of the most important parts of harvesting rainwater.
- Roof-Washing and First Flush System – Since your catchment surface will be exposed to the elements, it will surely become dirty. Just as you need to wash your car every now and then, your roof needs a good cleaning, too. Fortunately, you can let Mother Nature do the job for you with a roof-washing and first flush system. This essentially collects the first few inches of rain and discards it in a flush system, removing debris naturally at the beginning of every rain.
- Storage Tanks – Obviously, you will need one or more storage tanks to store your water. It is also your primary concern when it comes to keeping your system sanitary since it will be where water can stagnate.
- Conveyance System – The conveyance system is what connects the catchment surface to your storage tanks. This system might be as simple as a gutter leading from your roof to your tank, but if you have multiple tanks, multiple catchment surfaces, or underground storage, the system can get a little more complicated.
- Screening Mechanism – This essential part can be over the catchment surface, the storage tanks, or both. You will need some sort of screen to keep objects off your roof and out of your stored water. Contaminants like dirt and organic matter can build up on the roof, leeching harmful chemicals into your water. Similarly, they can permeate your water storage and cause disease.
- Water Filtration and Treatment – You can store as much rainwater as you like, but it will eventually become contaminated without proper filtration and treatment. There are many types of filtration and treatment discussed in the next section.
- Delivery System – The delivery system is responsible for getting the water out of storage tanks and into your glass. Some are as simple as gravity-fed taps, while others involve pressurized pumps and complicated piping.
Step 5. Acquiring and Combining the Right Supplies
Now that you have a basic understanding of harvesting rainwater, it’s time to combine the parts into a whole. There are many ways to do each step; simply choose the best fit for your needs. If you have trouble with any of the steps, see what each component looks like in this video:
- Build The Catchment Surface – This is your first step. Construct some sort of roof that will catch rainwater and slope it in an intentional direction. The best materials are roofing materials such as corrugated tin and other slick surfaces. Stone, concrete, and clay roofs will work as well, but you may lose water that soaks in. Wood shingles and asphalt shingles are not ideal, as rainwater will absorb toxins from these materials.
- Build a Conveyance System with a First Flush System – Determine how you will transport your water collected by the catchment surface. Your best bet is simple PVC piping that uses gravity. However, if you want to use a more sophisticated system, check out this article on conveyance systems. Install your first flush system in the middle of your conveyance system so that it intercepts water before it reaches your storage tanks. You can purchase one for about $35.
- Set Up Your Storage Tanks – Run the conveyance system into your storage tanks, which you can place either above ground or underground. There are many different types of tanks you can buy. Fiberglass and polypropylene are some of the more common options, but you can also build one out of wood or metal. If you choose those last options, you must have an inner lining that is FDA-approved so that harmful chemicals don’t leach out into your water supply.
- Screen Your Tank and Catchment Surface – Any type of screen will do to protect your system from small bits of organic matter like leaves. Also, consider building your system far enough away from trees that nothing will fall onto it.
- Set Up Your Water Filter and Treatment System – There are many options for water filtration and treatment. The first and easiest is to add chlorine bleach to your supply. The suggested ratio of chlorine to water is 2.3 fluid ounces of regular bleach for every thousand gallons of water. Another method is the ultraviolet method, which zaps harmful pathogens and renders them benign. The third is membrane filtration, which physically filters out unwanted particles. The most common membrane filtration system is a reverse osmosis filter.
- Hook Up Your Delivery System – Once all the other components are in place, set up your delivery system. There are a multitude of options available, from gravity-fed nozzles to hand pumps to complicated electric systems.
Step 6. Consider Upgrading to an Industrial Water Harvesting Unit
If you create a smaller system successfully, you may want to think about going bigger. There are two main pre-made water harvesting units that you can purchase: one that is stored above ground and one that is stored underground. Water tanks that live underground can add immense value to your home and land.
Underground water tanks will never be in danger of being tampered with, will not be in harm’s way during a natural disaster, and will not be unsightly or take up any property space.
You can find water cisterns that can be buried underground from many sellers ranging in sizes from 325 gallons to 5,100 gallons. As you may have already guessed, the larger the cistern, the higher the price.
However, a quality underground water cistern is a great long-term investment that will justify the cost you pay upfront. In-ground tanks or cisterns should be composed of polypropylene and may require an interior bracing structure.
If in-ground tanks are a little out of your price range, consider above ground rainwater storage units such as galvanized sheet metal tanks, concrete tanks, wood tanks, or polypropylene tanks.
Wood tanks must be lined with plastic, galvanized sheet metal tanks must be lined with a food-grade liner, concrete tanks that will be used to store water for consumption must be plastered with a high-quality material, and polypropylene tanks are typically the most affordable type of water storage tank on the market.
With a little bit of ingenuity and enough attention to detail to prevent disease, you can have a sustainable water source for a lifetime by building a rainwater harvesting system. Creating your own is not as difficult as it seems initially—after all, you most likely already have the roof of your house to use as a catchment surface.
Your ancestors have been doing it for thousands of years, and today, we know more than ever about how to make water safe. We also have more materials available than ever, which is why you should start planning your very own rainwater harvesting system today.
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Just remember, while rainwater might be a good thing, it is not the best thing for your body.
It has no minerals in it that your body needs.
I saw no mention of carbon filtering water.
While activated carbon is the choice one, ANY clean carbon is better than nothing.
robert alan searcy says
horseshit . ive been drinking rainwater off of my steel roof for 8 years . id rather drink birdshit than all of the chemicals that water companies use to render their shit palatable . i aint having any flu ? covid shots either . i’ll take my chances on what nature provides .
Good for you Robert. I feel the same. Helen
I also have large tarps to hang on tilted frames to collect rain.
If you have an asphalt shingle roof just layout as big a tarp as you have before rain (make sure that a couple of inches hangs over the peak) and use your gutters to collect the rain for you. That is my plan.
Elbert Jones says
Thank you for mentioning #2.Few people know that some states outlaw the collection of rain water. Even if it’s only used for watering plants.
i was interested in dew/fog harvesting instead
The article that linked to this one used the words “simple” and “constructed in a day” to describe rainwater collection. This here sounds quite a bit more complicated. It would take me several months on my own lol.
As far as water treatment I’d steer clear of chlorine bleach unless it was a last resort. I’d go with food grade hydrogen peroxide, unless I found out otherwise.
Thank you for the information.
Water like food and shelter are an absolute to life. Finding places and sources is a must. Also add sanitation to this list. After all what goes in comes out at some point. Write up a list of things. Review it and update it as you go along. Also take into account where you life in the good old USA. Example up north requirements and down south requirements are different water wise. Also take into account the disaster’s that may take place and adjust for it. Thanks.
Could I use a plastic to catch water sort of like an upside down umbrella over the container?
Best cheap way is a 55gallon barrel cut 2-3inch hole in top cover with mosquito netting. But it will crack in freezing weather. i use a garden hose attached to a suspended broken garden sprayer unscrew it and drain to a watering jug to water the garden. All gravity fed.
None of these ideas will work if you want PURE rain water without whatever is on your roof. It’s stunning that as of yet, not one method is available to catch rain water in a tank for human consumption. I’m wondering when someone will actually invent something that catches rain water that is SAFE to drink without boiling. As far as collecting off the roof, unless you have a roof that has NO materials that are harmful to human, the methods offered are not acceptable.
The article did mention having tin or metal roof as opposed to the asphalt or wood tiles.
There are ingenious people out there who can build the tank with a purification system, has to be. I’ve read H2o2 can be used to treat water, it’s chemical free.
Good luck to you
Hi Alice, here in Australia we have 3 really large water tanks which run our whole house – we don’t have town water. We don’t filter it or put any chemicals in it. It comes off tin roofs, we have gutter guards for debris but no filters on the taps and no chemicals. We’ve been doing that for the past 15 years without illness.
Lahaina Dilangalen says
I need to know the chemical treatment to make the rainwater safe for drinking pls.
City Prepping says
Thanks for the breakdown. I’m in the process of starting to build my setup. Great overview information here.