Easy Mosquito-Proof Rainwater Tank

Reader Contribution by Linda Holliday
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When warm weather finally reached the Missouri Ozarks this spring, I wondered if I’d have to drain my newest rain collection system before it became a mosquito nursery.

I like to encourage propagation of several beneficial lower life forms here, including earthworms, ladybugs, toads and lizards. Snakes, too, are most welcome. Mosquitoes, however, are not on my protected species list. Besides the diseases they carry, a swarm of pesky skeeters will send me bolting into the house, screaming about how I miss winter.

Last spring, my husband surprised me with a spiffy 425-gallon portable stock tank, one of the truly nicest gifts of my life. As we have no livestock, we instead leveled a space for the tank to catch rainwater under a downspout. Already into the drought of the century, though, it was August before any measure of moisture was in the tank. But, wow, was that nutritious rainwater ever appreciated when it finally arrived. My parched plants loved every drop.

The tank came with a threaded lid, which we replaced with a circle of window screen. My husband drilled numerous holes into the bottom of an old flour canister that fit nicely into the opening, and then set it atop the screen. The downspout, a section of 6-inch PVC pipe, sits inside the canister, which holds down the screen and can easily be dumped of accumulated leaves.

I fashioned a remarkably sun-proof cover for the tank by sewing together recycled bed sheets (on my trusty treadle, of course) and then painting the fabric with some leftover green enamel paint. The cloth cover shades the tank enough to help prevent algae growth, even in 100+ degree heat, and should extend the plastic tank’s lifespan.

I suspect mosquitoes hate the dome-shaped contraption as they are banned from their favored habitat – warm, still water. Did you know mosquitoes can reproduce in 10 days? In wet weather, even a cow’s muddy footprint provides a breeding ground for them. I am not so proficient in math, but calculate that to be a multitude of mosquitoes in very short order.

The 70-gallon stock tank I toted home from the local thrift store for $20 has no such domed lid. While conveniently exposed just outside my greenhouse door, I knew preventative mosquito measures would soon be necessary. I’d read about various techniques such as chemical dunks, goldfish and a slick of vegetable oil, but none precisely suited me.

As I lamented over what sort of device would keep winged bloodsuckers out, yet still allow me to readily dip in my 2-gallon watering can, my innovative husband showed up.

Incidentally, some years ago, I casually mentioned how I wished I had a scarecrow to keep the birds from stealing my squash seeds. Melding PVC pipe, galvanized metal fencing wire and 2- by 4-inch lumber, my husband erected a fully-clothed, spinning, life-sized mannequin with moveable arms that shook shiny pie pans at prospective intruders. The scarecrow worked well, not only for birds, but also terrified squirrels, rabbits and raccoons, eventually becoming an endeared family member. We named him Woody.

I can just throw a sheet over the stock tank, I mumbled as I remembered Woody.

My husband strode past me, made a bunch of noise in the shop and dashed back with an armload of tools and materials. “Here. Take a picture of this,” he said as he dumped the stuff on the ground.

That’s it? I wondered.

In less than 30 minutes, we assembled a simple, sturdy screen and plywood cover to keep the mosquitoes out and let me and my watering can in. I can still swish a huge handful of muddy radishes in the tank on my way to the kitchen and needn’t worry about increasing the bug population.

Build your own

To begin, lay a sheet of window screen material over the tank, leaving enough space open for your watering can. Fold under the raw edge a couple times on the open end to sturdy it. We used aluminum screen, but I suspect nylon screen would work just as well. Drape the screen over the tank sides, trimming it to allow an overhang of about 4 inches, and then lasso it securely with a strong rope. Use a razor knife to cut out an opening about 1/2-inch smaller than your downspout so it fits in snugly.

Next, cut a plywood top at least 4 inches larger than the width of the tank and length of the opening. Underneath, screw on strips of 1 1/2- by 1 1/2-inch scrap wood on three sides to hold the cover in place and to keep the plywood from warping. On top, screw on another wood strip as a handle and to keep the lid stiff over the screen. We repurposed an old plywood sign from a manufacturing company, so one side was already painted. I merely primed the remaining raw wood surfaces and called it good.

Already I can detect the mosquitoes’ agitation as they hover above the delightful water-filled tank, but can’t get in to multiply. While the cover and tank are not as lovely as our ol’ pal, Woody, they cost little and should safeguard our rainwater for many seasons.

Meanwhile, we are jotting down ideas for more rain collection systems, including the resourceful garden rainwater setupMother Earth News editor Cheryl Long wrote about in the August/September 2012 issue.

Photos by Linda Holliday

Linda Holliday lives in the Missouri Ozarks where she and her husband formed Well WaterBoy Products, a company devoted to helping people live more self-sufficiently off grid, and invented theWaterBuck Pump.