Simple rainwater harvesting garden system

Starting a rainwater harvesting system for your garden is a rewarding, eco-friendly project. The absolute simplest way to begin is by setting up a gravity-fed rain barrel system connected to an existing downspout.

Here is a straightforward, step-by-step guide to getting your first setup running:

1. Gather Your Materials

• Rain Barrel: A food-grade 50-to-80-gallon barrel (plastic drums work great; avoid containers previously holding chemicals or oil). Look for options with a built-in spigot and overflow valve, which you can find at local garden centers or via online hardware suppliers like The Home Depot.
• Cinder Blocks or Bricks: 2 to 4 sturdy blocks to elevate the barrel.
• Hacksaw: To cut your gutter downspout.
• Downspout Diverter or Flex Elbow: To direct water from the cut gutter into the top of the barrel.
• Mosquito Dunk / Mesh Screen: To keep pests and debris out of your water supply.

2. Choose and Prepare the Location

• Select a downspout near the garden beds you want to water.
• Clear and level a small patch of ground near the wall.
• Place your cinder blocks securely on the leveled ground. Elevation is key: raising the barrel by 1 ft to 2 ft creates enough water pressure for gravity to feed a garden hose or watering can through the spigot.

3. Modify the Downspout

• Measure the height of your elevated rain barrel against the downspout.
• Mark the downspout where the top opening of the barrel sits.
• Cut the downspout using a hacksaw.
• Attach a flexible downspout elbow or a specialized diverter kit so that runoff flows directly into the top mesh screen of the barrel rather than spilling out next to your home's foundation.

4. Install Mosquito Protection and Overflow

• Ensure the top of the barrel has a fine mesh screen to block leaves and mosquitoes from laying eggs.
• Drop a biological Summit Mosquito Dunks into the barrel if mosquitoes remain a concern; it's completely safe for plants, pets, and wildlife.
• Connect a short length of garden hose to the overflow valve near the top of the barrel and point it away from your house foundation to manage heavy downpours safely.

If you'd like, let me know:

• What is the approximate size of your garden?
• Do you plan to hand-water with a watering can , or hook up a soaker hose?

I can help you decide on the ideal barrel size and watering setup for your space.

A great way to start rainwater harvesting is to install a rain barrel under a downspout from your roof. It’s relatively inexpensive, simple to set up, and gives you a supply of rainwater for watering your garden between storms.

A simple starter system

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The basic idea is to collect rain falling on your roof, filter out leaves and debris, store the water in a covered container, and use it to water your plants.

How to set it up

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1. Choose a downspout

Pick one near the garden so you won't have to carry water far. A roof is an efficient collection surface, even for a small garden.

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2. Get a rain barrel

Start with a covered 50–60 gallon (190–230 L) barrel designed for rainwater collection. Choose one with a bottom spigot and a screened inlet.

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3. Prepare the base and overflow

Set the barrel on a firm, level base. A full 55-gallon barrel weighs about 460 lb (209 kg), so use a platform designed to support that load. Direct overflow away from your home's foundation.

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4. Connect and use it

Install a downspout diverter or suitable collection connection, add a leaf screen, and use the spigot to fill a watering can or connect a compatible low-pressure drip system.

What you'll need

How much water can you collect?

One inch of rain on 100 square feet of roof produces about 62 gallons (235 liters) before collection losses. Even a modest roof can fill a rain barrel quickly.

A few habits make the system work better:

• Empty and clean the barrel regularly, and keep mosquitoes out with a tightly sealed lid.
• In freezing weather, drain and disconnect the barrel to prevent damage.
• Direct overflow away from foundations and neighboring properties.
• Never drink untreated rainwater. For edible crops, avoid splashing untreated roof runoff onto leafy parts you plan to eat, and wash produce thoroughly.extension.colostate.edu+2

One important local note: If you're in Colorado, most qualifying households can use up to two rain barrels with a combined capacity of 110 gallons for outdoor watering. Check the rules for your property before building a larger system.extension.colostate.edu+1

For more detail, see the Colorado State University Extension rainwater harvesting guide.

Want to tailor it to your garden?

The best setup depends on your roof, space, and watering needs. Where would you put the system — under a house gutter, beside a shed, or somewhere else? I can suggest a simple layout and an approximate materials budget.