8.11 Building a Roof and Gutter Catchment System

Difficulty: Moderate · Time: about 1–2 days · Cost: about $150–$500 (one or two barrels, diverter, fittings)

A roof is the biggest water collector you own. One inch of rain on 1,000 square feet of roof yields about 620 gallons. Even a shed roof can catch more water than a family needs in a rainy week.

What you need

• Gutters and a downspout (or a tarp rigged to funnel water)
• Food-grade barrels (55-gallon drums or IBC totes that held food-safe contents), with lids
• A first-flush diverter: a vertical pipe section that fills with the first, dirtiest water before overflow goes to the barrel (buy one, or build one from PVC pipe, a tee, and a cap with a small drip hole)
• Fine mesh screen (window screen) to keep out leaves and mosquitoes
• Spigot and overflow fittings (bulkhead fittings), plumber’s tape
• Cinder blocks or a sturdy wooden platform to raise the barrels
• Hose or pipe to link multiple barrels
• Drill with hole saw

Tools: cordless drill, hole saw or step bit sized to your bulkhead fittings, utility knife or file, hacksaw (downspout and PVC), level, tape measure, ladder, pliers, screwdriver.

Steps

1. Check the roof. Metal roofs are best. Asphalt shingles work but add grit and some chemicals; avoid treated wood shakes and roofs with lead flashing for drinking water. Clean the gutters.
2. Check your local rules. Most states allow residential rain collection, but some limit volume or require registration. Look up your state’s rules.
3. Build the platform. Set barrels on level cinder blocks or a platform at least 12 to 18 inches high so a bucket fits under the spigot. A full 55-gallon drum weighs about 460 pounds; build accordingly.
4. Install the spigot. Buy the bulkhead fitting first; its package gives the hole size (often 1-1/8 to 1-3/8 inches for a 3/4-inch fitting). Match a hole saw or step bit to it.
   • Mark a spot 3 to 4 inches above the bottom, on a flat part of the drum wall, where the nut can reach from inside (through the open top or the large bung).
   • Drill slowly with a cordless drill. Let the bit do the work; plastic melts and grabs if you push.
   • Deburr the edge with a utility knife or file so the gasket sits flat.
   • Fit the bulkhead with a rubber gasket on the inside wall (and one outside if supplied). Snug the nut by hand, then a quarter turn with pliers. Overtightening splits the drum.
   • Wrap the spigot threads with plumber’s tape and screw it in. Use food-safe silicone on the gasket face only if the maker says to.
   • Leak-test with a few inches of water for 24 hours before you fill it. No drips, then fill. Sediment settles below the spigot, which is why it sits a few inches up.
5. Install the overflow: drill near the top the same way (bulkhead, gasket, deburred hole) and fit a hose that carries overflow away from the foundation, or into a second barrel.
6. Fit the first-flush diverter on the downspout. Size it at roughly 1 to 2 gallons per 100 square feet of roof. After each rain, open the drip cap and let the diverter empty so it’s ready for the next storm.
7. Screen the inlet so leaves and mosquitoes can’t get in. Keep the lid tight. Paint or cover translucent barrels to block light and prevent algae.
8. Link more barrels in series with a hose between lower fittings if you need more storage.
9. Treat before drinking. Rainwater is surface water. Boil or disinfect it (Sections 8.6 and 8.7). Untreated, use it for flushing, washing, and gardens.
10. Improvised catchment: in an emergency, stretch a clean tarp or plastic sheet at an angle with a low corner over a bucket. Rinse the tarp in the first minutes of rain.

Safety

• Disconnect and drain barrels before hard freezes. Ice cracks barrels and fittings.
• Keep lids tight and secure. Open barrels are a drowning hazard for small children.
• Don’t use barrels that held chemicals, even if washed.

Build sheet: Roof and gutter rain catchment

• Difficulty: Moderate
• Time: about 1–2 days
• Cost: about $150–$500 (one or two barrels, diverter, fittings)

Materials:

• Gutters and a downspout (or a tarp rigged to funnel water)
• One or two food-grade 55-gallon drums or a food-grade IBC tote, with lids
• A first-flush diverter (store-bought, or PVC pipe, a tee, and a cap with a small drip hole)
• Window screen for the inlet
• Bulkhead fittings, a spigot, an overflow fitting and hose, plumber’s tape
• Cinder blocks or a sturdy platform
• Hose to link barrels

Tools:

• Cordless drill with a hole saw or step bit sized to the bulkhead fittings
• Utility knife or file (to deburr)
• Pliers
• Hacksaw (for the downspout and PVC)
• Level, tape measure, ladder, screwdriver

Steps:

1. Check the roof (metal is best; no treated shakes or lead flashing for drinking water) and your state’s rain collection rules.
2. Clean the gutters.
3. Build a level platform 12 to 18 inches high, so a bucket fits under the spigot.
4. Drill the spigot hole 3 to 4 inches above the bottom with a hole saw sized to the bulkhead, deburr it, fit the bulkhead with its gasket inside, tape the spigot threads, and leak-test with a few inches of water for a day.
5. Drill and fit the overflow near the top. Route it away from the foundation or into a second barrel.
6. Cut the downspout and fit the first-flush diverter. Size it at about 1 to 2 gallons per 100 square feet of roof.
7. Screen the inlet, seat the lid, and paint or cover translucent barrels.
8. Link more barrels with hose between the lower fittings, if needed.
9. Label the barrel: treat before drinking (Sections 8.6 and 8.7).

Test it:

• Run a garden hose on the roof, or wait for the first rain. The diverter should fill first, and then the barrel.
• Check the spigot, bulkheads, and links for drips.
• Watch the overflow. It should carry water away from the house, not against the foundation.
• Open the diverter’s drip cap afterward and check that it empties.

Safety:

• Drain and disconnect before hard freezes.
• Keep lids tight. Open barrels are a drowning risk for small children.
• Never use barrels that held chemicals.
• Treat rainwater before drinking. Untreated, it’s for flushing, washing, and gardens.

To move stored rainwater without a pump, see Section 8.14.