How to Use Rain Barrels | Collect Rain, Water Plants

A rain barrel collects roof runoff and stores it for garden watering, saving tap water and lowering your bill.

One inch of rain on a 500-square-foot roof sends roughly 110 gallons of water down the spout — enough to fill two standard barrels. The trick is catching that water without flooding your foundation, growing mosquitoes, or cracking the barrel in winter. Here is the step-by-step system that works, from base to spigot.

Where to Put a Rain Barrel and How to Prepare the Base

Place the barrel directly under a downspout and as close to the garden as possible — every extra foot of hose adds drag. A full 55-gallon barrel weighs about 450 pounds, so the ground underneath must be dead level and firm enough not to shift when the barrel settles.

Building the platform

• Dig out 1–2 inches of turf, tamp the soil, and add a 1-inch layer of gravel or sand for drainage.
• Set concrete blocks, pavers, or a gravel pad flush to the surface. The base should be wider than the barrel footprint.
• Elevate the barrel 12–24 inches using cinder blocks or a purpose-built stand. That height gives enough gravity pressure to fill a watering can or run a short soaker hose. A lower barrel works, but the flow will be slower.

Connecting the Downspout to the Barrel

Two methods work, and both start with the same warning: check that no heating cables or electrical wiring run inside the downspout before cutting anything.

Diverter method (cleanest for most setups): Bore a hole into the downspout or cut a short section out, install a rain barrel diverter, and attach a flexible hose from the diverter to the barrel’s top inlet. The diverter sends water into the barrel until it is full; excess pours down the regular downspout.

Cut-and-elbow method (simpler, less adjustability): Cut the downspout roughly 6 inches above the barrel top, then attach a flexible elbow that angles into the barrel opening. This method is cheaper but cannot automatically redirect overflow back into the downspout.

Assembling the Barrel and Adding the Spigot

Most entry-level barrels come with pre-drilled holes and a basic hardware kit. Insert threaded rubber seals into each hole, then screw in the spigot (top hole) and the drain piece (bottom hole). Use metal or rubber washers on both sides of the barrel wall, and run a bead of waterproof sealant around each connection before tightening — a slow drip here is the most common leak source.

Attach the overflow hose to the valve at the top of the barrel. Route that hose toward a garden bed, a tree, or a splash block, but never toward your home’s foundation — unmanaged overflow causes erosion and basement seepage.

Install the mesh screen over the top opening to catch leaves, sticks, and nesting critters. Caulk any tiny gaps around the screen frame to block mosquitoes. Add an anti-larval tablet containing Bacillus thuringiensis (Bt) to kill any eggs that slip through — one tablet per barrel, effective for about 30 days.

Find a tested model with all the right fittings in our guide to cheap rain barrels that work.

How to Use the Water and Avoid Trouble

Rain barrel water is not potable. It collects bird and squirrel waste from the roof and is untested for microbial safety. Use it only on the soil at the base of non-edible ornamentals — flowers, shrubs, established trees. Even then, avoid overhead spraying on edible leaves; soil-level watering only.

The first few gallons that run off your roof after a dry spell carry the most buildup. Either let that initial flush run past the barrel (a first-flow diverter does this) or discard the first batch manually.

Use stored water within 1–2 weeks to keep it fresh and clear. Empty, scrub, and rinse the barrel at least once a year — warm climates do not get a pass on this. A long-handled brush, detergent, and a 3-percent bleach solution work well.

The one winter rule you cannot skip

Drain the barrel completely before the first freeze. A barrel packed with ice expands and cracks. Store it upside-down on the platform or move it into a garage. If you cannot move it, tip it on its side and leave the spigot open.

Discarded water from a drained barrel can be used immediately on the garden — it is safe and will not shock plants.

Rain Barrel Basics: A Quick Look