Build a Rain Barrel That Actually Lasts Through July

Quick answer: A 55-gallon barrel under a downspout fills in a single decent storm. The hard part is storage, not supply. Raise it two feet, screen it, give it an overflow, and plan on more than one barrel if you're feeding anything bigger than a 4x8 bed.

The math nobody does first

One inch of rain on 1,000 square feet of roof gives you about 623 gallons. Run that against your downspout. If it drains a quarter of a 2,000-square-foot roof, that's 500 square feet. A half-inch shower sends roughly 155 gallons down the pipe.

Your barrel holds 55.

So the barrel isn't the bottleneck. It overflows in the first twenty minutes and the rest runs into the yard. That's why a second or third barrel is the best upgrade you can make.

Now the demand side. A garden wants about an inch of water a week, which works out to roughly 60 gallons per 100 square feet. A 4x8 bed is 32 square feet, so it drinks around 20 gallons in a normal week and more in a July heat wave. One full barrel runs that bed for two to three weeks. If you've built the bed from our under-two-hundred-dollar plan, one barrel is a fair match. Two beds, plan on three barrels.

Your zone and season decide how this goes

In the Southeast and much of the East, summer storms refill you every week or two. One or two barrels carry you through.

In the Mountain West, the Southwest and inland California, summer is the dry season. You collect in spring and fall, and the water you stored in May is what you've got in July. Bigger storage matters more there. Check your hardiness zone for your frost dates too. In zones where the ground freezes, drain the barrel and disconnect it before the first hard freeze. Ice will split a plastic barrel and crack a spigot.

One more check before you buy anything. A few states limit how much rainwater you can collect, and some homeowner associations have opinions about barrels. Colorado, for example, caps residential collection at two barrels totaling 110 gallons. Call your county extension office or read your state's rules. Ten minutes beats a letter.

What it costs, honestly

These are ballpark numbers. Shop your own area.

• The barrel: free to about sixty dollars. Food-grade 55-gallon drums come from bottlers, car washes and farm suppliers. Make sure it never held anything but food or drink. A used one with a tight lid is the sweet spot.
• Spigot fitting: a 3/4-inch bulkhead fitting with a hose-thread spigot, about ten to twenty dollars.
• Downspout diverter kit: twenty to forty dollars, or build one with a cut downspout and an elbow.
• Mesh screen, overflow hose, Teflon tape, silicone: another ten to twenty.
• Cinder blocks for the stand: four to six blocks, a few dollars each.

Call it eighty to a hundred and fifty dollars for a one-barrel system. And be honest with yourself. Most municipal water costs well under a penny a gallon, so the barrel won't pay itself back in one summer. What you're buying is a reserve that doesn't depend on a water bill or a watering restriction. Rainwater also has no chlorine in it and plants seem to like it. Tomatoes in particular hate swinging between bone dry and soaked, and a steady barrel supply helps you even that out. Our piece on tomatoes that taste like water covers why.

Build it

1. Set the base first. Water weighs 8.3 pounds a gallon. A full barrel is over 450 pounds. Level a patch beside the downspout and stack cinder blocks two high, so the top sits 18 to 24 inches off the ground. Wet soil settles. A barrel that tips over on a Tuesday is a bad Tuesday.

2. Drill the spigot hole. Use a hole saw or step bit sized to your bulkhead fitting. Place it three to four inches up from the bottom. That leaves a little sediment room under the outlet. Thread the fitting through, wrap with Teflon tape, seal around it with silicone, and let it cure a day.

3. Cut the top inlet. Cut a hole in the lid, or in the barrel's top, big enough for the downspout drop. Cover any opening with fine mesh, fiberglass window screen works, and secure it. This is the part that keeps mosquitoes out. A neglected barrel with open water is a mosquito nursery. Screen it, and check it a couple times a season.

4. Add the overflow. Drill a second hole near the top, fit a short hose or a 1-inch pipe, and run it six feet or more away from your foundation. Skip this and the first storm tests your basement.

5. Connect the downspout. Cut the downspout a few inches above the barrel, add the diverter or elbow, and hold it with a couple of sheet-metal screws. A diverter is nicer because it sends water in until the barrel is full, then sends the rest back down the pipe on its own.

6. Fill it, check it, fix leaks. Fill it by hose the first time. If the spigot weeps, snug the nut and add silicone.

What goes wrong

Weak pressure. A barrel on a two-foot stand gives you under one pound per square inch. That's enough to fill a watering can and run a soaker hose slowly. It's not enough for a sprinkler or most drip emitters. Choose a soaker hose, or a watering can, or add a small pump later.

Algae. Sunlight grows it. Use an opaque barrel, dark blue, black or green, not a clear one.

Dirty roof water. Your first few minutes of runoff carry shingle grit, bird droppings and pollen. For flower beds and soil-level watering it's fine. If you're growing leafy greens, water the soil and keep spray off anything you're about to eat. Don't drink it and don't use it on food if your roof has treated wood shakes or copper. Your county extension office can tell you what's safe for your roof type.

The empty-barrel surprise. You water heavily the first hot week, drain 55 gallons in days, and then it doesn't rain for a month. Plan with the weather forecast, not the hope.

Leave it better than you found it

Chain a second barrel to the first. Connect them with a short hose from the overflow of the first into the top of the second, and set both at the same height. You double storage for the price of a fitting and a hose.

Then give the garden a deep soak every few days instead of a light sprinkle daily. Roots go where the water is, and a deep soak sends them down. A good barrel plus that habit is how you keep the garden alive in August when the neighbor's lawn is brown and his sprinkler is running.

That's the whole project: a barrel, a stand and a Saturday. After the first big rain, when you hear the water rushing into your own tank and know it's yours, you won't need anyone to tell you it was worth it.