How to Harvest The Rain: An Update with Test Results

Yes, even from a shingle roof.

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It’s a real buzzkill to watch all these prepper videos on YouTube show you how to build a rain harvesting system, only to realize that you can’t do it. Why? The rainwater from your shingle roof contains an ungodly amount of deadly toxins and poisons. Or maybe it doesn’t. But it probably does. We kept getting different answers. We emailed some rain harvesting specialists a few years ago and asked them if there was any way to do it. They said, “Don’t bother…” That felt conclusive.

Like I said, a real buzzkill…

And then there’s all the survival and homesteading guides that kinda tell you how to build a rain harvesting system, but not really…

My family brainstormed, but we kept running into walls. Then finally, we started piecing together a plan. After all, we’re not interested in drinking rainwater every day. We don’t want to spend tens of thousands of dollars on cisterns, pumps, and special plumbing. We don’t want to ditch the grid just yet. We just want a simple backup water source for emergencies, and now would be the time. If you’ve been going through the same frustrations, hitting the same dead ends, then maybe this post will help. We’re laying out the plan in maximum detail. We barely got any rain last week, and our barrels have already filled up. 100 gallons.

Since our first update, we got our lab results back from Tap Score. They analyzed the water for 100+ contaminants common in roofwater. It’s clean, with one exception, and we already found a solution. If you just want the results, then scroll down to the last section. Otherwise, start here.

Let’s get into it:

First, dig out your foundation. Add paver base and paver sand. This step helps you level the ground and provide a good substructure for your barrels. You want to dig below the topsoil and into the harder clay. If it’s too hard, soak the area with a hose and leave it for 24 hours. You can also use a pickaxe, but don’t swing it overhead like they do in the movies. Use it more like a hoe. Letting a 5 lb mattock drop into the ground will help break it up. Use a level to get the bare dirt as even as possible, but know that the paver base helps the most. Tamp it down.

We used 24 x 16 inch pavers for the base. They’re heavy as hell (50 lbs), but they’re worth it to create a large, even footprint. Lay cinderblocks on top. Two cinderblocks with one turned perpendicular match the paver size. The cinderblocks give you the clearance for hooking up hoses, filling up buckets, etc. You’ll put another layer of pavers on top for a smooth surface.

Remove the bottom section of gutter. You’ll probably have to unscrew downspout straps. You might be able to simply reconfigure your gutter pieces like the image shown above. We placed our barrels 2 feet away from the house to help protect the foundation. We wound up using a hacksaw on a downspout to get the right length. It can be frustrating to cut gutter, but it works. We tried aviation snips, but a hacksaw provided the cleanest cut. If you don’t want to mess with cutting gutter, you can buy precut lengths from places like Gutterworks.

Make sure to measure the gutter heights. You want a few inches of space between the barrel and the gutter exit. Remember that your gutter will be heading down at a 75-degree angle. Don’t use a 90-degree elbow.

Water will pool…

Some people skip this step and just buy diverter kits. We couldn’t find a diverter kit with consistent reviews. Biggest complaint: They’re either flimsy, or they don’t collect much rain during light showers. We’re building for extreme droughts, which means a free-flowing gutter. We also skipped the first flush. My full illustrated guide talks about them, but we opted for something simpler.

You can buy barrel nets that fit over the entire top part of the barrel. They’re easy to put on. All the debris from the first gutter gush ends up on the net. You just pull it off and shake it. Your barrels will also have a mesh screen over the top entry hole. It’s two layers of protection.

You can buy rain barrels from almost any hardware or big box store now. We decided to go with Epoch. They have a strong reputation. They use upcycled food barrels. Ours arrived clean, with all the parts already installed. We could’ve drilled out the holes ourselves, but it can be a real hassle if you’re also digging a foundation and working on other projects. These are tough barrels that will last a long time, and that’s the goal. They’ll take a beating. Remember, these things will be holding hundreds of pounds of water when they’re full.

You can link the barrels at the top and bottom to ensure they fill at the same time. Just add hose splitters to the faucets. Get a short hose for the top link. You can cut it and then add a female hose repair to the other end. You technically only need one splitter, but two means you can draw water from either barrel. The second barrel is probably going to have the cleaner water.

Unfortunately, most preconfigured barrels come with tiny garden hose outlets for the overflow. They’re not going to handle a major storm or a flash flood if you’re using a free-flowing gutter. Companies assume most people will be using a diverter kit. If you’re using a full gutter, then you need a bigger overflow. We did the math and arrived at a 2-inch hose. Combined with our two-barrel system, it can handle up to 3 or even 3.5 inches of rain per hour. Believe it or not, even during a drought, you can expect some pretty intense surges. That’s part of the problem. The rain comes in short bursts and flash floods. It’s not steady. You don’t want a flood to send water gushing over the top of your barrels. It’ll soak your foundation and ruin all that hard work. It’s not easy to find a 2-inch heavy duty hose, but we finally got one from Gloxco with a male NPT nipple. It’ll fit right into a 2” bulkhead union. For that, we’re drilling a 3-inch hole on the backside, just the first barrel.

A closeup of the hose splitters. Pretty standard. But if you want a heavy duty one that’s lead-free, try Morvat.

The hardest part was coming up with a way to filter the roofwater. Most pump systems we looked at were expensive and impractical on a budget. Then we got the idea to use a battery pump. It would give us the pressure and gpm needed to push the water through inline hose filters. While a battery pump will ultimately overheat and die if you run it like this for hours, we’re not doing that. We’re running the pump long enough to fill up a bucket for emergency drinking water. Or we’re running it long enough to feed our plants with a soaker hose. That’s 10-15 minutes max. The filter setup looks complicated, but it’s not that bad.

• First, add a 60-mesh hose filter to the pump intake. This step keeps grit from the barrel water from ruining the pump. The phrase “60 mesh” means 60 openings per inch of screen. You can go as high as 400, but don’t. If the screen is too fine, it can choke pumps and deflect water.

• Next, a Camco tastepure filter (20 micron) acts as a sacrificial first defense. It removes finer sediment. It also strips out some of the VOCs and heavy metals. Its main job is to protect the other filters.

• The Envig Catalytic KDF55 uses a stronger type of carbon that strips out a lot more VOCs and heavy metals.

• The Clear2O does a final sediment mop-up to catch anything that got through the first two filters, including any carbon particles.

These filters don’t strip out any viruses or bacteria. They do prefiltering for our gravity-fed setup at the end. You can add a little bleach (about 1 ounce) to each full barrel to help knock out those threats early. Be careful. Bleach can interact with roof runoff to create toxic byproducts. You can also use HOCl. It’s safer, more effective, and it won’t ruin your clothes.

The good news:

All of these filters use garden hose thread. They come with garden hose attachments. So does the pump. You don’t have to fuss with adapters.

Simple.

You can go the extra mile in your prefilter setup by adding a Sawyer Tap. It’s a tight little .1 micron filter that also features a garden hose thread for easy attachment. The .1 micron filter blocks 99.99 percent of bacteria and other threats like Giardia and Cryptosporidium. It also stops microplastics and fiberglass dust that can shed from a shingle roof. One of the only things it doesn’t stop: viruses. (For that, we use the gravity system.) Even better, this filter costs around $30 or $40, and it doesn’t need replacements. You can clean it by reversing the water flow. Adding this element brings our system into peak performance. The gravity-fed system gets nice, clean water to do a final round of purification.

One last thing:

The more filters you add, the more backpressure risk you add to your pump. That can strain the motor and cause damage. Bypass this problem by adding another hose splitter on the pump outlet. Route one spigot into your filter lineup. Route the other back to your barrel. That way, your pump pushes as much water into the filters as they can handle. The excess goes back to your source. That’s especially important if you’re going to use submicron filters.

Problem solved.

Battery pumps offer convenience, but you might wind up in an emergency with no power and no water. That’s why we got a manual pump. It took a long time to find something capable of delivering the right pressure to push through 3-4 different inline filters, but we finally landed on the Bosworth Guzzler. There’s a model with a short handle for around a hundred bucks. It’s moderately hard to operate. We shelled out the extra money for the upgraded version with an extended handle, because… who knows? Maybe we’ll get injured. Maybe our kid will wind up needing to run the pump. The upgraded version makes operation way easier.

If you order a Guzzler, you can choose garden hose threads for the native ports. With the manual pump, you have a lot more control over the pressure and flow. You’ll still probably want to add a 60-mesh sediment filter to the inlet.

The filter line feeds into a bucket. We got 2-gallon and 5-gallon foodsafe buckets. Some days, you’ll want to filter several gallons. Other days, you’ll just want something light. For the hoses, we went with Camco 4-ft premium RV drinking hoses. They’re foodsafe. You don’t want to run standard garden hoses into your pump or your bucket. They can reintroduce contaminants.

On the filter end, if you need any adapters, look for ones made with lead-free brass or 304 steel. That way, you keep it all clean.

The inline filters remove heavy metals and VOCs, along with sediment. They don’t remove viruses, bacteria, parasites, etc. Even the Sawyer Tap .1 micron filter can’t get the viruses, even though it stops the rest. That’s where the gravity-fed systems come in. We spent a long time untangling all the claims and ad copy to find out which gravity filters actually do what they say.

Ultimately, we went with Alexapure.

Since our first update, we added yet another stage here: HOCl treatment. We added 1/3 cup of HOCL (100-200 ppm) to every 1 gallon of water to kill any remaining viruses or bacteria. You probably don’t want to add HOCl to your gravity-fed system, because it’s corrosive over time. So, add a second container. We’re using a 2-gallon sports cooler. Just open your spigot and pour it right in.

Then add the HOCl.

The Lab Test Results

We sent a sample of our filtered rainwater to a lab for testing. We used Tap Score’s “advanced rainwater test,” which looks for more than 100 different toxins including heavy metals, VOCs, and bacteria.

And…

Our sample looks clear across the board, with one exception. Although the lab found no E. coli, they did detect bacteria. We figured out why. Unchlorinated water will almost always trip a bacteria test. Going forward, we’re going to use HOCl (a chlorine-based compound) as a final treatment in the water. If you’re not familiar, it’s an extremely effective germ killer that’s safer than bleach.

(But you can still use bleach…)

HOCl isn’t great for carbon block filters, so we emptied the water into a final container, a regular 2-gallon sports cooler, and that’s where we added the HOCl, at roughly 2/3 cup with a 200 ppm solution. You add the HOCl. You stir. You wait about 30 minutes. You test with strips. If you’ve still got 3-10 ppm HOCl in your water, then it should be safe to drink. Virtually all viruses and bacteria are dead, and the remaining HOCl will protect your water for at least a day or two. We’re sending another sample to the lab. We’ll see how things go.

You can see the first round of results below.

It’s some pretty clean water:

Our conclusion:

This setup works. We probably won’t be drinking rainwater every day, and definitely not until we get the final results back from the second sample, but we feel good about using it during an emergency.

The entire setup costs about $1,000. It’s a fraction of what a full system would cost if you installed a metal roof and hired professionals. You can knock that price down even further if you don’t mind buying cheaper barrels and installing your own faucets. The biggest cost lies in the pumps. You could probably install something like this system for $600 if you went with an ordinary pump. You’d just need to find a way to power it for off-grid use. That’d be doable. The battery-powered pumps offer convenience and portability, but they’re not essential.

A basic cost breakdown:

Used DIY foodgrade barrels: $100 each.
Construction materials: $100
DIY gravity filter bucket: $200
Filters: $150
Pump: $50

If you can't afford this on a single budget, consider crowdsourcing it. A small group could share pumps and filters.

Wells can run dry. Reservoirs take a long time to recharge. After fifteen minutes of rain, we had dozens of gallons of water.

We made it safe to drink.

Mission accomplished?