If you live in a region that gets a lot of rain, you’ve probably considered making use of your natural resources and catching rainwater for drinking. But how do you make your rainwater safe for drinking? You’ll find the answer in this “how to filter rainwater” guide.
📌 Key Takeaways:
- Harvesting rainwater is a great way to reduce your water bills by taking advantage of what nature provides for free.
- There are 4 recommended filter stages to make water from a rain harvesting system safe to drink:
- Pre-tank filter
- Sediment filter
- Carbon filter
- UV water purifier
- Alternatively, use an RO system for an all-in-one filtration solution for rainwater, or save money with a water filter pitcher or countertop filter.
Table of Contents
🚰 How to Filter Rainwater: 4 Filter Steps
So, you’ve got your rainwater harvesting setup ready to go, with a decent-sized water storage tank, and safe, suitable roofing for the rainwater to run down before collecting in the tank.
Now, what sorts of filters should you be using to filter your rainwater? We recommend the following:
Step 1: Pre-Tank Filter
The first filtration stage should occur before water even reaches the rainwater collection tank.
Downspout debris filters and leaf guard filters are the best filters to install in your rainwater harvesting system, to filter the water as it travels down the drainpipe to the storage container. These filters trap large debris like leaves, rocks, and other materials that could be blown or washed into the gutters.
You’ll likely need to clean out or replace these filters regularly, so read the manufacturer’s instructions carefully.
Step 2: Sediment Filter
While a pre-tank filter will prevent large objects from entering the rainwater collection tank, it won’t actually clean the water, and nor will it remove smaller sediment like sand, silt, soil, and other debris.
For this, you need a dedicated sediment filter.
Sediment filters are usually installed as inline filters along your water line, but you can also use a countertop water filter that has the ability to remove sediment. This may be more suitable if you collect rainwater in your rainwater harvesting system, then bring it by bucket into your home.
Step 3: Carbon Filter
Another great choice for filtering rainwater is a carbon filter.
Like any water supply, rainwater carries a distinct taste and odor that you might find unpleasant. Carbon filters are the best filters available for not only improving water quality, but providing better-tasting and smelling water, too.
The most affordable, convenient activated carbon filtration system for rainwater is a water filter pitcher. Just pour your collected rainwater into the pitcher’s upper chamber, then wait for the water to filter through into the bottom chamber.
Many countertop filters also use an activated carbon water filter, and typically filter bigger batches of water than pitchers.
Step 4: UV Purifier
The final filtration step in all rainwater harvesting systems should be a UV filter.
Because harvested rainwater isn’t chlorinated or disinfected with any other method, you can’t guarantee that your water won’t carry bacteria, viruses, and other harmful pathogens from the surrounding environment. Ultraviolet light kills microbiological contaminants, making it the ideal solution for treating potentially contaminated rainwater.
UV filters can be installed directly at your water line or as a final stage to some countertop water filtration systems.
UV light can only penetrate clear water, so you’ll need to pre-treat turbid rainwater with a sediment filter if necessary.
All-In-One Filter: Reverse Osmosis System
If you want to avoid using multiple separate filter stages, the most convenient means of filtering rainwater is to use an all-in-one reverse osmosis system.
Countertop reverse osmosis units are the best option for rainwater filtration. These systems are placed on your kitchen countertop and designed for treating water in batches.
Simply add a batch of rainwater collected from your tank to the RO system, then switch the machine on. The water will flow through a sediment filter, an activated carbon filter, and a semi-permeable membrane, reducing more than 99.99% of total dissolved solids (TDS) with membrane filtration.
Reverse osmosis is the most thorough filtration process available today, so RO systems are an ideal choice if you don’t want to take your chances and want to be reassured that everything is removed from your rainwater for drinking.
Cheapest Option: Water Pitcher Filter or Gravity Countertop Filter
Don’t want to spend money on multiple filter stages or a reverse osmosis filter? Use a water filter pitcher or gravity countertop filter instead.
📌 Water pitchers cost less than $100 upfront and less than $50 per year to maintain. Countertop gravity filters are a bit more expensive upfront – about $200-$400 – because they hold more water.
These filters are easy to use: just pour water into the top container, then allow it to filter into the bottom chamber. The water can then be dispensed or poured from the device, ready for drinking.
Make sure your countertop filter or pitcher filter is capable of removing microorganisms. If it isn’t, you’ll need to boil your water after filtering it to ensure it’s safe to drink.
Related Article: 18 top Methods for Off Grid Water Filtration and Purification
🧫 What Does Rainwater Contain?
Now we know how to filter rainwater, let’s briefly touch on the common rainwater contaminants.
You might assume that rainwater is pure enough to drink as it is, but this is rarely the case. Rainwater often contains harmful chemicals and pollutants, including PFAS, heavy metals, bacteria, viruses, dust, smoke, nitrogen, and other airborne particles.
So, filtering your rainwater is essential if you want to be certain that you’re not ingesting anything that’s harmful to your health.
💡 We’ve shared a whole article discussing the contaminants commonly found in rainwater if you’re looking for more information.
📖 Rainwater Harvesting Best Practices
There’s no way to completely prevent rainwater contamination, since a lot of contamination occurs in the atmosphere.
With that said, there are a few best practices to implement if you want to avoid polluting your water during rainwater harvesting:
- Collect water straight from the sky. Ideally, collect rainwater that doesn’t touch any other surfaces before entering the container. This reduces the likelihood of contamination from guttering, roofing, and other materials.
- OR ensure your roof material is safe. Collecting rainwater from a roof is tempting since you can direct the flow of water easily to your tank, allowing for more efficient collection. But if you do plan to harvest rainwater from a roof, make sure the roof is pre-painted corrugated metal. Shingle, thatch, terracotta tiles, and other common roofing materials are known to leach natural tannins and chemicals into rainwater, so they’re not safe to use.
- Use a food-grade water tank. Make sure the storage tank you use is designed for storing water for drinking. You want to avoid contaminating your water with plastics or metals from the tank, even if you plan to filter the water before you drink it. Galvanized metal and BPA-free plastic with vinyl liners are good choices for an above-ground tank. Plus, make sure the water tank is completely covered, preventing dead insects, leaves, and other pollutants from getting in.
- Clean your gutters regularly. If you’re collecting rainwater from a gutter system, clean out your gutters at least twice a year. This will prevent leaves and other organic material from getting into your soon-to-be drinking water. You should also wash out your rain barrel to keep it clean and free from microorganisms like bacteria and algae.
Related Article: Where is it illegal to collect rainwater?
❔ How to Filter Rainwater: FAQ
What is the best filter for rain water?
The best filter for rain water is an RO system because it provides every type of water treatment required to remove microorganisms, chemicals, metals, and more, ensuring high-quality drinking water.
How do you filter rainwater in the wild?
You can filter rain water in the wild by making an outdoor water distillation system. Dig a hole, then place a container (like an empty coffee can) in the hole and stuff damp green plants around the outside of the can. Place plastic wrap over the hole, then place a small pebble in the middle of the wrap to make a dip. As the sun heats the hole, the moisture from the plants will rise, then condense as it hits the underside of the plastic wrap and drip into the container.
How do you purify water from a rain barrel?
The best way to purify water from a rain barrel is to boil the water or treat it with UV purification to kill bacteria and viruses, then run the water through a countertop filtration system or a water filter pitcher to remove physical contaminants. If your rainwater is sediment-heavy, you’ll need to filter it with a sediment filter before any other treatment.
Can Brita filter rainwater?
No, Brita filters are unlikely to make a difference to the quality of your rain water supply. Brita’s products are designed to treat disinfected drinking water from a faucet, and remove a handful of contaminants, including chlorine, asbestos, and lead. Since rainwater contains PFAS, heavy metals, bacteria, viruses, dust, smoke, nitrogen, and other airborne particles, a Brita filter won’t have much effect on your water quality. If your rainwater isn’t potable, Brita won’t make it safe to drink.
Is it safe to drink filtered rainwater?
Yes, it’s safe to drink filtered rainwater, as long as your rainwater filtration system effectively removes all the contaminants in your water to safe trace levels. If you plan to use rainwater as drinking water, we recommend treating it with a reverse osmosis system or a water distiller, which will eliminate nearly everything that could be in the water.