Rainwater collection and purification basics
Catch rain in a barrel for the garden, and know how to make it safe to drink when you have to.
- Difficulty
- Beginner
- Time
- An afternoon to set up
- Cost
- About $50–150 for one barrel setup
- Region
- Anywhere, with Florida notes
- Safety
- High: read the safety box first
This guide is a draft and hasn't been reviewed yet.
A roof is a big funnel. Every inch of rain on 1,000 square feet (93 m²) of roof gives about 620 gallons (2,350 liters). One barrel fills in a single summer storm.
[AI illustration: a dark green rain barrel on cinder blocks under a downspout, with a screened lid and a spigot]
Is it legal?
Rain barrels are legal in Florida and in most US states. A few states limit how much you can collect, and some homeowners’ associations have rules about how barrels look. Check yours before you buy. [placeholder: your county or HOA rules, if any]
Set up a barrel
You need:
- A food-grade barrel, 55 gallons (208 liters), dark or opaque so algae can’t grow
- A downspout diverter or a cut downspout with a flexible elbow
- Fine mesh screen over every opening
- A spigot near the bottom, and an overflow pipe near the top
- Cinder blocks to raise it up
Steps:
- Level the spot next to a downspout and stack the blocks. Raising the barrel gives better pressure at the spigot and room for a watering can.
- Fit the spigot near the bottom and the overflow near the top. Point the overflow away from your house’s foundation.
- Screen every opening. In Florida, mosquitoes can breed in standing water within a week. No gaps.
- Add a first-flush diverter if you plan to treat the water for drinking. It dumps the first, dirtiest rain off the roof before the barrel fills.
- Connect the downspout and wait for rain.
[AI illustration: a diagram of a rain barrel with labels for the screen, first-flush diverter, overflow and spigot]
Roofs and gutters
- Metal roofs give the cleanest water.
- Asphalt shingles are fine for the garden. For drinking, treat the water and get it tested.
- Don’t collect for drinking from treated wood shingles, roofs with lead flashing, or anything freshly painted or coated.
- Clean the gutters before storm season and after big storms.
Making it safe to drink
Treat rainwater the same way you’d treat any water of unknown quality after a storm.
- Let it settle, then filter it. Pour off the clear water and run it through a clean cloth, paper towel or coffee filter.
- Boil it, the best option. Bring it to a rolling boil for 1 minute, or 3 minutes above 6,500 feet (1,980 m). Let it cool. Store it in clean, covered containers.
- Or disinfect it with bleach if you can’t boil. Follow the amounts in the safety box above, by strength. Bleach does not kill every germ as reliably as boiling.
Don’t pour rainwater into stored tap water or bottled water. It can contaminate water that was already safe.
Hurricane season
- Before a storm: fill clean, covered containers with tap water for drinking. Keep the rain barrel for flushing and washing.
- After a storm: if there’s a boil notice, treat rainwater the same way as tap water: boil or disinfect.
- Secure the barrel. A full one weighs over 450 lb (204 kg), but an empty one can blow away. Fill it or strap it down.