Collecting rainwater is one of the most practical things a homeowner can do. Here's how to start simple and scale up as far as you want to go.
Rainwater harvesting sounds more complicated than it is. At its simplest, it's a barrel under a downspout. At its most developed, it's a whole-property water collection system that meaningfully reduces your dependence on municipal or well water for irrigation, sanitation, and — with proper treatment — drinking.
Most people should start with the simple version and build from there. Here's how to do both.
Why Collect Rainwater?
Resilience: A rain barrel gives you a water source that doesn't depend on municipal infrastructure, power, or well pumps. During an extended outage or water disruption, even a few hundred gallons of collected water is meaningful.
Utility: Collected rainwater is excellent for garden irrigation, livestock watering, toilet flushing, and general non-potable household use. With appropriate filtration and treatment, it can be made potable.
Cost: Rainwater is free. Reducing irrigation draw from a well or municipal supply has real long-term value.
Legality: Rainwater collection is legal in most U.S. states, though some have restrictions on quantity or use. A few western states have historically limited collection due to water rights law — check your state's current regulations before building a large system.
Level 1: The Single Rain Barrel
This is the right starting point for most people. A single 55-gallon barrel connected to one downspout costs $30–80 in materials and takes an afternoon to set up.
What You Need
- A food-grade 55-gallon barrel (repurposed food barrels work well — look for barrels that previously held juice, syrup, or food-grade liquids; avoid chemical barrels)
- A downspout diverter kit (available at hardware stores, ~$15–25)
- A spigot/faucet fitting for the barrel
- A fine mesh screen for the top opening (to keep out debris and mosquitoes)
- A short section of overflow hose
- Basic tools: drill, hole saw, wrench
Setup Steps
1. Choose your location. Pick a downspout that drains a significant portion of your roof. Position the barrel close to where you'll use the water.
2. Elevate the barrel. Place it on cinder blocks, a sturdy wooden platform, or a purpose-built stand. Even 12–18 inches makes a meaningful difference in gravity-fed flow rate.
3. Install the downspout diverter. This fitting redirects water from your downspout into the barrel when filling, and automatically bypasses to the original downspout when the barrel is full.
4. Install the spigot. Drill a hole near the bottom of the barrel, insert the spigot fitting, and seal with waterproof sealant. Let it cure fully before filling.
5. Cover the top. Secure fine mesh screen over the barrel opening to filter debris and prevent mosquito breeding. This is not optional.
6. Add an overflow outlet. Drill a hole near the top and attach a short hose that directs overflow away from your foundation.
First Barrel Tips
- Label it clearly — non-potable water should be marked as such
- Empty and clean it annually — sediment accumulates at the bottom over time
- Disconnect and drain before freezing temperatures — water expands when it freezes and will crack your barrel or fittings
- A 55-gallon barrel fills faster than you expect — a 1,000 sq ft roof section can fill it in less than an inch of rain
Level 2: Multiple Barrels in Series
Connect barrels using a short length of hose between fittings installed near the bottom of each barrel. Water fills the first barrel, then flows through the connecting hose to fill the second, and so on. Install your spigot on the last barrel in the series for the cleanest draw.
Three 55-gallon barrels give you 165 gallons — enough for meaningful garden irrigation or a substantial non-potable emergency reserve. Keep barrels on the same level so water distributes evenly.
Level 3: A Dedicated Collection Tank
An IBC tote (Intermediate Bulk Container) is a 275 or 330-gallon plastic tank inside a metal cage, designed for bulk liquid transport. Used food-grade totes are available for $100–200 and are an excellent value for rainwater storage.
One IBC tote gives you roughly five times the capacity of a single barrel. Two totes connected in series gives you 550–660 gallons — a serious water reserve. Setup is similar to barrels: connect to a downspout diverter, elevate for gravity pressure, screen the inlet, and add overflow management.
Level 4: A Full Roof Collection System
A complete rainwater harvesting system collects from your entire roof, routes water through gutters to a central collection point, filters it before storage, and stores it in a large tank or cistern.
System Components
- Collection surface: Your roof. Metal roofing is ideal. Asphalt shingles work but may introduce some contaminants.
- First-flush diverter: Discards the first flow of water from each rain event — which carries the most debris and contaminants — before routing cleaner water to storage. Essential for any system where water quality matters.
- Gutters and downspouts: Standard gutters work. Keep them clean.
- Pre-storage filtration: A mesh or sediment filter before the tank removes particulates before storage.
- Storage tank: A large polyethylene tank or underground cistern. Sizes range from 500 to 10,000+ gallons.
- Post-storage treatment: For potable use, add appropriate filtration and disinfection.
Sizing Your System
Multiply your roof's square footage by average monthly rainfall in inches, then multiply by 0.623. This gives you approximate monthly collection in gallons.
Example: 1,500 sq ft roof × 3 inches of rain × 0.623 = approximately 2,800 gallons per month.
Making Collected Rainwater Potable
Rainwater picks up contaminants from your roof, gutters, and storage system. For drinking water use, it needs treatment in three stages:
- Sediment filtration — remove particulates
- Carbon filtration — remove organic compounds and improve taste
- Disinfection — kill biological contaminants via UV treatment, chlorination, or a quality ceramic/hollow fiber filter rated for biological removal
A gravity filter system handles all three stages effectively for household-scale use with no power required.
Tools Worth Considering
- Platypus GravityWorks 4L Filter System — gravity filtration for treating collected rainwater to potable standard
- Sawyer Squeeze Water Filter — portable filtration for smaller quantities
- Water Purification Tablets — disinfection backup for treated rainwater
- Family Gravity Water Filtration System — higher-capacity gravity filtration for household use
- 30-Gallon Home Water Reserve System — for households building a dedicated water storage setup
The barrel and tank components are widely available locally — hardware stores, farm supply stores, and used equipment sources are good places to start. We focus on the filtration and treatment side where quality and reliability matter most.
Preparedness isn't about fear. It's about capability. A rain barrel is one of the most practical things you can add to a home — and it scales as far as you want to take it.
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