Home / Guides / Irrigation, Soil & Fertility Timing

Rainwater Harvesting Calendar

Collecting rain works best when the barrel is set up before the rains you want to catch and drained before the freeze that would split it.

When should you set up a rain collection system?

Set up ahead of your region's wetter months, not in the middle of them. Look at local rainfall records from the National Weather Service or your state climatologist to see when rain usually arrives and when the dry stretch that makes stored water valuable begins.

Pick a spot under a downspout on firm, level ground. A full barrel is heavy, and a base that settles will tip it. Raising the barrel a bit makes it easier to fill watering cans and gives gravity-fed hoses some pressure.

Quality changes with the season. Pollen, leaves and bird droppings land on roofs in spring and fall, and the first rain after a dry spell carries more of it. Many systems divert that first flush away from the tank so cleaner water goes in.

What should you check on the collection surface?

Roof material matters. Penn State Extension and other land-grant sources treat roof runoff as suitable for ornamental use and, with care, for gardens, but they also note that roofing and gutters can contribute contaminants. Old asphalt shingles, treated wood shakes and metal with certain coatings raise more questions than clean metal or tile.

Clean gutters before the wet season and use a screen or first-flush arrangement to keep leaves and debris out. Ask extension whether your state has guidance on using roof water on edible crops, and favor drip or soil-level watering so water does not splash on leaves you will eat.

Think about overflow. A full barrel in a storm sends water straight to the ground near the foundation unless you direct it. Point overflow lines to a garden bed or a drainage area away from the building, and check local stormwater rules.

How do you keep mosquitoes and algae down?

Cover every opening with fine mesh and check the overflow for gaps. Mosquitoes need open standing water, so a tight lid and screened inlets and outlets address most of the problem. Opaque barrels in shade also limit algae.

Check the screens every spring and after storms. Empty and scrub the barrel at least once a year, and keep stored water for irrigation only, not for drinking.

In dry regions, rainfall may come in a few big events. A larger tank captures more of those events. In wet regions, smaller storage that you use up often keeps water fresh.

How should you use the water through the season?

Use stored water within a reasonable time instead of letting it sit for months. Many gardeners draw from the barrel first and switch to the hose only when it runs out. Because a barrel empties quickly, it is smart to match it to a small bed or a few containers rather than a whole field.

For example, if you have a single raised bed, you can estimate how much you need by watching how many cans you use per watering in a normal week. Then add up your barrel capacity and see how many days it covers. That measuring habit is more useful than any formula.

What about winter and legal questions?

In cold climates, drain the barrel and disconnect the diverter before the first hard freeze, and store it upside down or open to the sky. Frozen water expands and splits plastic and fittings.

Some states regulate or encourage rainwater collection, and rules can cover storage size, use and permits for larger systems. Check your state and local rules, and consider a licensed professional for any system connected to plumbing.

How big a system do you actually need?

Rain collection is limited by roof area and rainfall. A small roof in a dry region will fill a barrel only a few times a year, while a large barn roof in a wet region can fill a large tank quickly. Work through your own numbers using local rainfall records before buying storage.

For small gardens, one or two barrels often match the need for hand watering. For larger plots, cisterns or ponds fed by roof runoff may fit better, and those can fall under state permits or dam safety rules. Ask before you build.

What maintenance does the system need through the year?

Clean gutters and screens before the rainy season and after leaf fall. Check diverters, hoses and overflow lines for cracks and blockages. Inspect the base for settling.

Scrub the inside of the barrel when it is empty, and rinse well. Replace worn parts and check the lid seal. A short seasonal routine, written on a calendar, keeps the system working and keeps mosquitoes and algae in check.

Last reviewed: November 2026. Educational information, ranges only. Confirm timing with your county extension office.

More in Irrigation, Soil & Fertility Timing

• Greywater Irrigation Calendar
• Soil Solarization Timing
• Biofumigation Calendar
• Cover Crop Termination and Planting Calendar
• Green Manure Timing Calendar
• Crop Residue Management Calendar