Collecting Rainwater
Every inch of rain that falls on a 1,000 square foot roof produces over 600 gallons of water. Most of it goes down the drain. A rain barrel system captures that free resource and puts it directly into your garden.
Check your state's rules first
Rainwater collection is legal in most states, but a few have restrictions on how much you can collect or how it can be used. Check before you buy anything. A quick search for “[your state] rainwater collection laws” will give you a clear answer in under two minutes.
Unrestricted or encouraged:
Most US states. No limits on collection volume for residential garden use.
Check carefully:
A small number of states have had historical restrictions — particularly western states where water rights are complex. Most have loosened these laws in recent years but verify your current state status.
How a rain barrel system works
The basic setup is simple: a downspout from your roof carries rainwater into a barrel with a spigot at the bottom. You draw water from the spigot by gravity — no pump needed — and use it to fill watering cans or connect a soaker hose directly to the barrel.
Most barrels include a diverter kit that installs inline with your existing downspout. The diverter automatically sends overflow back to the downspout once the barrel is full, so you don't have to manage it. Installation takes about 30 minutes with basic tools.
What size do you need?
The honest answer: more than one barrel. A single 55-gallon barrel is a good start and it fills up fast in a decent rainstorm — a half-inch of rain on a 1,000 sq ft roof generates over 300 gallons, which means your barrel fills completely and you're losing the rest down the drain.
Sizing by garden size
Enough for several days of watering between rains for a small setup.
A linked series gives you a week of watering capacity in most climates.
Serious storage. Covers longer dry spells without running out.
Connecting multiple barrels
Linking barrels together multiplies your storage without needing multiple downspout locations. The most common method is a daisy-chain overflow setup.
- 1Install the first barrel at your downspout with the diverter kit as normal.
- 2Drill a 3/4" hole near the top of barrel 1 on the side facing barrel 2.
- 3Install a bulkhead fitting in that hole and connect a length of 3/4" flexible hose to barrel 2's inlet.
- 4When barrel 1 fills, water overflows through the connecting hose into barrel 2.
- 5Continue the chain as needed — each additional barrel adds to your storage.
- 6Make sure barrel 2 (and any subsequent barrels) are at the same height or lower than the previous one — water won't flow uphill.
Screening and mosquito prevention
Any opening in the barrel needs a screen to keep debris and mosquitoes out. Most barrels come with a screen over the inlet, but check and replace it if it's damaged. If you're building your own setup from a salvage barrel, cover every opening with fine mesh window screen and secure it with a hose clamp or bungee cord.
Mosquitoes can't breed in water that moves or that's properly covered. As long as your barrel is sealed and screened, it's not a mosquito risk. If you're concerned, Bti dunks (Bacillus thuringiensis israelensis) are a non-toxic biological larvicide that can be dropped into any open water.
Getting water out: gravity flow and hose connection
Most barrels have a 3/4" spigot near the bottom. For gravity flow to work with any pressure, the barrel needs to be elevated — even 6–12 inches on cinder blocks makes a real difference in flow rate to a hose or soaker line.
For a soaker hose directly off the barrel, you'll need the barrel elevated at least 12–18 inches and the hose run downhill or flat — soaker hoses don't work well uphill against gravity pressure. For a drip system, elevation of 2–3 feet gives reasonable pressure.
If you want to run a longer hose or fill a watering can faster, a small submersible pump ($25–40) placed inside the barrel runs off a standard extension cord and pumps water significantly faster than gravity alone.
A note on water filtration
Rainwater collected off a roof is great for garden irrigation — it's naturally soft, unchlorinated, and slightly acidic in a way plants like. It is not, however, drinking water. Don't use it for drinking or food prep without proper filtration and testing.
For garden use, basic screening is sufficient. If you want to build a simple DIY filtration system to remove sediment and organic material before the water reaches your barrel, we cover that in a separate guide — a layered sand, gravel, and activated charcoal filter that can be built from hardware store materials for under $15.
Winter prep
If you're in a climate that freezes, drain and disconnect your barrels before the first hard freeze. Water expands when it freezes and will crack a plastic barrel or burst a metal one. Disconnect from the downspout, open the spigot to drain completely, and store indoors or under cover until spring.