Top 7 Mistakes To Avoid When Harvesting Rain Water

Harvesting rain water should be a priority for any serious prepper or gardener.

Did you ever go on a long hike, then find yourself parched with thirst? The need for water catches up with you quickly.

If the city water or your well shut down for a week, would you be able to survive or would your house become unlivable? Stockpiling guns, gold and food is a good idea – but having a way to hold on to water is of paramount importance.

Fortunately – in most climates – God gives us a ready supply from above if we can just figure out how to capture it. I’ve been harvesting rainwater on a budget for years and have figured out what works and what doesn’t.

Today I’ll share my top 7 mistakes to avoid when harvesting rain water.

I’ve also put them into a video version:

Let’s jump into the mistakes, starting with a very common one.

Mistake #1: Make It Expensive

Harvesting rain water DOESN’T need to be expensive!

If you have a larger budget and plan on keeping your homestead for a while, there are excellent systems with diverters, filtration, underground cisterns and pumps – which are great – but not necessary if you’re having a hard time rubbing two nickels together. You can do this on the cheap. I’ve even converted trash cans to rain barrels:

harvesting rain water

Though after I set up a couple of homemade rain barrels at my old homestead, I realized I could capture a lot more water for free by creating ponds. Instead of digging proper ponds with expensive liners, I got a pair of solid old hot tubs from a local pool company. All I had to pay was a delivery fee (these suckers were too heavy for me to move!), then find PVC caps to fit the pipe holes in them. Direct a gutter into a hot tub and you’ll hold hundreds of gallons of water. I planted mine with edible and useful aquatic plants and threw in some local “mosquitofish” and gold fish to eat any mosquito larvae that might show up. I also scored another hot tub by the side of the road, taking my total up to three.

The total capacity was roughly 1200 gallons between them and I had plenty of water to keep my gardens alive through any drought.

Mistake #2: Let the Mosquitoes In

Mosquitoes can take a great idea and make it a health hazard. As new viruses sweep around the world, people are rightly concerned about the danger of harvesting rainwater improperly. Even old tires hold enough water to breed mosquitoes, so a rain barrel has the capability of breeding thousands of the bloodsuckers.

The best way to keep them out is to keep your rain barrels or cisterns covered so mosquitoes don’t lay their eggs. I’ve covered mine with screening in the past, then had the screening get pushed in during a heavy downpour, which then let mosquitoes lay eggs, leading to a bunch of squiggling larvae.

harvesting rain water

I cover compost tea barrels and rain barrels with screening but it isn’t foolproof.

A friend with an excellent rainwater harvesting system much bigger than my own told me that he had issues with mosquitoes occasionally due to openings, but he had used “mosquito dunks,” which are a non-toxic mosquito-killing product comprised of bacteria that sicken and kill the larvae. Just desserts!

I tried it and they worked like a charm; however, the best method is just to keep things closed.

Mistake #3: Choke The Flow

This was my first rookie mistake.

I built a pair of rainbarrels and carefully attached spigots to the bottoms of them, hoisted them a few feet above the ground on stacked cinderblocks, then directed in the gutters. After the first rain I was excited to give them a test, so I put a bucket under the spigot and opened it fully. To my great irritation, the faucet aperture was too small. It would take about three to five minutes to fill a bucket. That’s an eternity if you’re hoping to get some watering done, and it meant I used those rain barrels a lot less than I would have if they had generous faucets.

A friend has a great big PVC outlet on the side of one of his 1,000 gallon cisterns that allows out a blast of water when cranked open.

That’s what you want – don’t use fiddly weenie faucets!

Mistake #4: Go Too Small

Don’t go too small!

Just like you don’t want little faucets, you should also avoid small storage capacity. Though I thought rain barrels were a great idea at first, I realized that they filled in just a few minutes under the gutters, then overflowed for the rest of a rain storm. That’s when I got thinking about ponds and then added hot tubs. The rainwater harvesting capacity of a roof is incredible.

The University of Arizona reports “A one-inch rain will collect 600 gallons from a 1,000 square foot roof, while 4,500 square foot lot will receive 2,800 gallons!”

They further share how you can calculate the water catching power of your roof:

  1. Measure the square footage of the collection area (for example a roof that is 30 feet wide x 50 feet long = 1500 sq. ft.)
  2. Multiply the area by the amount of rain in inches
  3. Multiply that number by 0.623 (that is the quantity of water in gallons one inch deep in one square foot of space)

= number of gallons that can be collected.

More capacity is better!

Mistake #5: Miss The Power of Swales

This is a common mistake.

Like your roof, the ground also catches a lot of water, yet much of it is lost due to evaporation and run off.

Using swales as a method of rainwater harvesting makes a lot of sense. Swales are just ditches or indentations deliberately constructed to slow the movement of water and allow it to soak in.

Here’s a swale running through our cocoa orchard:

harvesting rain water with a swale

Though this isn’t a method for harvesting rainwater you can drink, swales hydrate the soil deeply and effectively, particularly on sloping ground. Using swales creates passive irrigation downhill from the swale and can transform a dry area into an oasis.

Find the contour of your land and dig some swales, then plant fruit trees or gardens or both around them. I’ve seen roadside ditches filled with green vegetation at the bottom during a drought that has burned all the surrounding grass brown.

If you’re harvesting rainwater to grow food, look into swales!

Mistake #6: Muck it Up with Algae

Algae is the enemy of clean water.

Though it won’t hurt your plants to dump scummy green water on them (in fact, they like it), it’s not appetizing or helpful if you hope to filter and drink the water you catch.

Like mosquitoes, the best way to beat algae is not to let it into the system to begin with.

Harvesting rainwater in black covered containers will keep algae from becoming a problem. They are tiny plants which photosynthesize for survival, so if you cut off the sunlight you cut off the algae. I’d rather use darkness than an algacide if I have my choice.

Mistake #7: Not Harvesting Rain Water at All!

The biggest mistake in harvesting rain water… is to NOT harvest rain water at all.

You need very little infrastructure to get started.

Heck, throwing a trash can under a gutter is better than nothing – and digging a swale isn’t tough either. Just mulching after a rain will trap moisture in the soil and make your plants happier. If you have more of a budget, get some big cisterns going.

Where I live in Central America, almost every house has a cistern for harvesting rain water in case of hurricanes or a loss of city water. Water is life – get harvesting now and you’ll be in a much safer place. Without water, you and your survival gardening plans will come to nothing.

Good luck and thanks for reading. May your plans prosper and the rains fall abundantly.



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Access my step-by-step blueprints specifically guiding you through how to build the most robust and reliable rain catchment system for not only capturing 1,000’s of gallons of potable water, but how to filter, heat and preasurize it so that it can replace your well, or the city water in an emergency.

Click here to check out my Ultimate Rain Catchment System Blueprints



About David The Good

David The Good is a naturalist, author and hard-core gardener who has grown his own food since 1984. At age five, he sprouted a bean in a Dixie cup of soil and caught the gardening bug. Soon after, his dad built an 8’ by 8’ plot for him and David hasn’t stopped growing since. David is the author of four books, writes a regular column for The Ag Mag in North Central Florida, is a Mother Earth News blogger and has also written for outlets including Backwoods Home, Survival Blog and Self-Reliance Magazine. You can find his books on Amazon here. David is a Christian, an artist, a husband, a father of seven, a cigar-smoker and an unrepentant economics junkie who now lives somewhere near the equator on a productive cocoa farm. Visit his daily gardening and survival blog here: The Survival Gardener And for lots more gardening info, click here and subscribe to his often hilarious YouTube channel.

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6 Responses to “Top 7 Mistakes To Avoid When Harvesting Rain Water”

  1. Cathy McNama Says:

    So the previous owners put I a 500 gal septic tank that is used ONLY for water collection. It has a drain so it does not overflow. I don’t use it much in the last few years. What precautions should I take to make sure it will be safe to drink a crisis.


  2. JJM Says:

    Choke the flow: Good point – small drain = small volume. Would be good to note that elevation of the water source plays a significant aspect. Water pressure = slightly less than 1/2 PSI (actually 0.43 PSI) per foot of drop in a gravity fed system. When full, a 3′ tall barrel will provide only 1.5 PSI at the spigot BUT the same full barrel lifted 3′ above ground with a hose or pipe run to ground level will provide 3 PSI at ground level. But realistically, water is very heavy and any means to raise the barrel elevation MUST be VERY sturdy to avoid collapse.


  3. David Kapler Says:

    Thanks for the article. Do you know a good source or two for rain harvesting equipment?


    • Chet Says:

      Our guide covers a lot of our favorite sources for building a really robust system. Its written by Scott Hunt, who’s a SUPER legit engineer when it comes to anything water. I’d recommend that resource if you’re serious.


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