Getting Started
What a rain barrel is, how it works, and whether it suits your roof and garden.
Grow a greener garden with rainwater from your roof
Catch roof rainwater in a barrel and water your garden, lawn and ornamental plants — free, soft water, straight from the sky.
Non-potable use only: ornamental garden and lawn watering. Not for drinking, cooking or bathing.
Rain Barrel Calculator
How much rainwater can your roof catch? Enter your roof size and rainfall.
Typical range 75–95%. Losses come from splashing, evaporation and gutter overflow.
Overflow is the storm water left over after your barrels are full.
Results
- Roof area
- —
- Gallons per inch of rain
- —
- Gallons per storm
- —
- Gallons per year
- —
- Barrels needed to catch one storm
- —
- Barrels filled by one storm
- —
- Overflow — water beyond your barrels
- —
Formula: gallons = roof area (sq ft) × rainfall (inches) × 0.623 × (efficiency ÷ 100). First flush, when on, deducts 10 gallons per 1,000 sq ft from each storm. The yearly total is before first-flush losses, since the number of storms per year varies. 1 gallon = 3.785 litres.
Estimates only — check local rules. Rainwater from this calculator is for non-potable, ornamental garden and lawn use only.
Start here
Setup & Install
Choosing a barrel, placing it, fitting a diverter and linking barrels together.
Troubleshooting
Slow flow, leaks, smells, algae and mosquitoes — fixes that actually work.
Equipment
Barrels, stands, diverters, filters, hoses and screens — what to buy and what to skip.
Latest guides
Best Roof for Rainwater Collection: Metal vs. Asphalt Shingle vs. Tile
The best roof for rainwater collection is metal. A smooth metal roof collects the most water, at over 90 percent efficiency, and it sheds debris quickly, so the water that reaches the barrel is cleaner than water from any other roof. Asphalt shingle is the most common roof, and it is good enough for barrel […]
How to Water the Garden With a Rain Barrel (Soaker Hose + Gravity Pressure)
Water the garden with a rain barrel by raising the barrel 18 to 24 inches on a stand, running a soaker hose from the spigot to the bed, and letting gravity do the work. The water flows slowly at soil level, straight to the roots, with no pump, no electricity, and no sprinkler. A watering […]
Why Is My Rain Barrel Water Smelly / Green / Slimy? (Causes + Fixes)
Rain barrel water smells bad, turns green, or feels slimy when three things combine: debris rotting at the bottom, sunlight feeding algae, and water sitting still for weeks. Fix all three — drain and scrub the barrel, shade it from direct sun, and use the water regularly — and the smell, the green colour, and […]
DIY Rain Barrel Under $50: Food-Grade Drum, Parts List & Build
You can build a DIY rain barrel for under 50 dollars using a used food-grade 55-gallon drum, a brass spigot, a downspout diverter, and a mesh screen. The total for the parts below is about 45 to 50 dollars, and the build takes two to three hours with basic hand tools. A store-bought rain barrel […]
Can You Collect Rainwater in Texas? Rules, Limits & Rebates
Texas encourages rainwater harvesting, and collecting rainwater from your own roof for non-potable garden use is generally allowed in Texas, with conditions set by state law, local city ordinances, and your homeowners association. That is the short answer, but it is not the whole answer: the details depend on where you live in Texas, how […]
Rain Barrel vs. Rain Tank: Which Size Is Right for Your Roof?
For most homes, a rain barrel is the right choice for watering ornamental beds, and a rain tank is the right choice only if you want to water a whole yard or a large lawn. A 55-gallon barrel costs 50 to 100 dollars, fits against a wall, and covers a bed or two. A 250-gallon […]