Best Rain Barrel for Garden Watering: What to Look For

What Makes the Best Rain Barrel for a Garden

The best rain barrel for garden watering is a dark, opaque, food-grade plastic barrel of about 55 to 60 gallons with five things built in: a screened inlet, a spigot that accepts a garden hose, an overflow outlet you can attach a hose to, a lid that fastens, and a way to link a second barrel. Set it 12 to 36 inches off the ground on a solid base. Those features matter more than shape or styling, because they decide whether the barrel fills cleanly, drains usefully and stays free of mosquitoes. Everything below explains how to judge each one.

Feature	What to look for	Why it matters
Capacity	About 55 to 60 gallons, with a linking port	Small roof areas fill one barrel in a single storm
Material and color	Food-grade HDPE in a dark color	Dark walls block sunlight and algal growth
Inlet	Screened top or screened diverter inlet	Keeps out debris and egg-laying mosquitoes
Spigot	Garden hose thread, mounted low	Lets you fill a can or run a hose by gravity
Overflow	A port that accepts a hose	Sends excess water away from the foundation
Lid	Fastens securely	Clemson lists a fastened lid as a safety precaution
Base	Blocks, pavers or a platform	A full barrel weighs about 460 pounds

Size the Barrel to Your Roof

Capacity depends on the roof more than on the garden. Clemson Extension gives the working formula: multiply the roof area in square feet by 0.623 to get the gallons that run off in a one-inch rainfall. Wisconsin Extension rounds the same math to about 600 gallons for every inch of rain on 1,000 square feet of roof.

Roof area draining to the downspout	Gallons from 1 inch of rain
100 square feet	about 62
250 square feet	about 156
500 square feet	about 312
1,000 square feet	about 623

Set those numbers beside a typical barrel. Most rain barrels are built from a 55-gallon drum, and Clemson notes that as little as 100 square feet of roof may fill one quickly. Rutgers offers another way to picture it: a home with 800 square feet of roof sheds roughly 600 gallons in a 1.25 inch storm. A single barrel captures a small share of that, which leads to two practical conclusions. First, every barrel needs a real overflow. Second, if you want more stored water, buy a model with linking valves so you can chain barrels together with short hoses and add capacity later.

Check local rules and any homeowner association restrictions before you install one, since some places regulate rainwater collection or where a barrel may stand.

Barrel Types and Shapes Compared

Shape is mostly a question of where the barrel has to fit.

Type	Best for	Watch for
Standard round barrel, 55 to 60 gallons	One downspout feeding beds and containers	Stands out from the wall
Tall narrow or flat-back barrel	Tight side yards and patios	Small footprint under a heavy load; fasten it
Collapsible fabric barrel	Renters and seasonal use	Must be drained and stored for winter like any barrel
Decorative or planter-top barrel	Front yards	Check that it still has a screen and an overflow
Linked barrels	Larger roofs and bigger gardens	Each connection needs to stay tight

A tall narrow rain barrel deserves an extra note, because people shopping for one are usually working with a strip of ground beside a wall. Clemson points out that a 55-gallon barrel weighs over 450 pounds when full and should be securely fastened when it is elevated. With a slim barrel the same weight rests on a smaller base, so a level pad and a strap to the wall matter even more.

For material, choose a food-grade barrel. Rutgers describes the typical unit as a 55-gallon high density polyethylene (HDPE) food-grade barrel. If you convert a secondhand drum, use one that held food products. Pick a dark color too, since Clemson notes that a dark barrel prevents sunlight penetration and algal growth.

Stand Height and Water Pressure

A rain barrel has no pump, so gravity does the work. Clemson’s rule is that every 1 foot of elevation adds approximately 0.4 psi, and barrels are typically raised 12 to 36 inches. That puts a barrel on a stand somewhere around 0.4 to 1.2 psi from the stand alone, enough to fill a watering can or trickle water through a short hose to a nearby bed.

New Mexico State University’s research on gravity-fed drip gives useful context. Each 2.31 feet of water above an emitter supplies 1 psi, so a drum with its water level 6 feet above the soil delivered about 2.5 psi. Standard drip systems are generally designed for 10 to 30 psi, and household water usually arrives above 30 psi. In those trials, drip tape and certain low-flow emitters still worked at 2.5 psi, so a barrel can run a small drip line if you choose parts made for low pressure. Our guide to drip irrigation kits for small gardens explains what to look for.

Height helps in a second way. Penn State Extension says to raise the barrel high enough that you can easily put a bucket under the spigot. A barrel on the ground with a low spigot is awkward to use, and awkward barrels sit full and unused. For hand watering, pair the barrel with a can that fills quickly, as covered in how to choose a watering can.

Build the base for the load. A full 55-gallon barrel weighs about 460 pounds according to Rutgers, and Penn State puts the upper figure at 500 pounds. Use concrete or cinder blocks, pavers or a sturdy wooden platform on level ground.

Spigot, Overflow and Screens

These three fittings separate a good barrel from a frustrating one.

The spigot should accept a standard garden hose and sit low on the barrel. Penn State describes a spigot placed 6 to 12 inches from the bottom. Water below the spigot cannot drain by gravity, so a lower mounting leaves less behind.

The overflow is not optional. Rutgers advises attaching a hose to the overflow drain and directing excess water at least 6 feet from the foundation if the building has a basement. Send it to a lawn or garden bed where it can soak in, and keep it off driveways and walks. A downspout diverter is a tidy alternative, because it returns water to the downspout once the barrel is full.

Screens decide whether the barrel breeds mosquitoes. In the warmest weather some species go from egg to adult in 5 to 7 days, so standing water needs attention within a week. Rutgers recommends covering the top with tightly fitting window screening, keeping a screen on every opening at all times, and leaving a hose 8 to 10 feet long attached to the overflow, since that length discourages mosquitoes from traveling up it. Wisconsin Extension adds that water should not stand in the barrel for more than five to seven days. If larvae do appear, products containing Bti are labeled for rain barrels.

Using Barrel Water on Vegetables

Roof runoff picks up whatever has settled on the roof, animal droppings included, so Nebraska Extension says not to drink it, cook with it, give it to pets or wash garden produce in it. On whether it belongs in the vegetable garden, extension services differ. Wisconsin does not recommend it for vegetables, and Penn State says it is best used on inedible plants such as lawns and flowers. Penn State specifically warns against watering edibles from old tar-and-gravel or asbestos shingle roofs, treated wood shingles or shakes, copper roofs, or roofs with a zinc anti-moss strip.

Rutgers tested harvested water and published a set of practices for gardeners who do want to use it on food crops:

1. Clean the barrel with a 3 percent bleach solution before the season.
2. Treat stored water monthly with 1/8 teaspoon of bleach per gallon, which Rutgers puts at about one ounce for a 55-gallon barrel.
3. Wait about 24 hours after adding bleach before using the water.
4. Apply water only to the soil, by drip or with a can, and keep it off the plant.
5. Water in the morning, and do not harvest right after watering.

Rutgers also says the water should, at a minimum, be tested for E. coli through a health department or certified lab. If raccoons visit your roof, Nebraska Extension advises against collecting the water at all. For how much water beds need through the hot months, see the summer garden watering schedule.

Winter Care

Freezing water cracks barrels. In fall, drain the barrel and disconnect it from the downspout and hose. Then either store it in a garage or shed, or leave it empty with the spigot open. Rutgers adds that a barrel left outside can be turned upside down and secured. Reconnect it in spring after cleaning the screen and rinsing out sediment.

Quick Recap

• Look for a dark, food-grade barrel of about 55 to 60 gallons with a screen, hose spigot, overflow port, fastening lid and linking valve.
• One inch of rain yields about 0.623 gallons per square foot of roof, so 100 square feet can fill a barrel.
• Raise the barrel 12 to 36 inches on a base built for 460 pounds, and expect roughly 0.4 psi per foot.
• Run the overflow at least 6 feet from a basement foundation and keep every opening screened.
• Apply barrel water to soil only, and drain and disconnect the barrel before winter.