Harvesting the Rain: How to Properly Collect Rainwater for Reuse in the Garden

By Barbara H. Shaw
Published: November 1, 2017 | Last updated: February 6, 2020 08:59:40
Key Takeaways

Whether it’s out of necessity, to lower your water bills, or to help the planet, harvesting rainwater can be rewarding. However, there are a few things to consider before installing a system.

I lived some months in Palau, in the Pacific, where rainwater was the only source of fresh water. Faulty pipes served the town, but out on the coral isles. Every shelter collected water from the thatched or metal roof and stored it in a shiny steel tank with a mesh filter on top.


If you’re considering your own collection system, check local regulations. In the US, some jurisdictions in dry, western states have old laws requiring all water in certain districts to be under the control of a water master. Many areas of Australia, however, either allow or require it on all new construction, while it’s regulated by building codes in Canada. In India and other countries, newer laws make rainwater harvesting mandatory for new buildings.

After you check local laws, look at your goals. The idea is to create a long-lasting, safe, and efficient water collection system for your own use, with inexpensive materials using basic construction skills. While harvesting water from roofs using gutters is simple, storage solutions such as rain barrels requires more thought.


Collecting Rainwater in Your Area: Questions to Ask

  • The most basic question before beginning any upgrade project is: Will this be cost-effective? In the case of water, is the local supply safe, dependable, and affordable? If so, would the cost of a system pay for itself?
  • Will our gutters catch the rain, or can we create and attach some at bottom edge of the roof? Is the roof a good collection surface? The ideal roof material for collection is metal as it is long lasting, non-porous, and non-toxic. But other materials are fine, including slate, tile, thatch, planted surface, or shingles of wood or asphalt.
  • How will we keep stored drinking water clean and free of insect larvae and other pathogens? A mesh filter on the intake side and a tight cover are generally all that’s needed, though a little chlorine bleach, iodine, or bromine salts will discourage live things and maintain a higher level of cleanliness.
  • Who is going to maintain the system once it’s in place? What sort of care will it need? How much water do we need to store, and at what times of year? What quality of water do we need—drinking water with filtration or just water for washing, cleaning, or watering a garden? Grey water has already been used for washing or cleaning, but has its uses such as for animals, flushing, and irrigation.

Read More: 50 Shades of Grey Water


With water, energy, food, and other commodities, it’s invariably less costly to cut waste than to create a new source. Drip irrigation is a good water-conservation investment, as is flow control for a shower or tap and a low-flow toilet. If water is a serious issue in your area, don’t waste it flushing toilets.

Consider the advantages of composting toilets to create safe fertilizer from excrement. Simple plans for better systems are available online. In Palau, a teenager built a composting toilet as a science project, invited guests to use it, and vastly improved the output of the family fruit trees. By my next visit, officials had built composting toilets in parks there.


Read More: Can You Remove Salt from Sea Water to Irrigate Your Plants?

Why Rain Water?

Rain offers the cleanest naturally occurring water available, created by nature’s evaporative distillation process. Only airborne dust particles and man-made pollution can taint it. Where the air carries smoke and ash or airborne pollutants from industrial processes involving fossil fuel, rain is not clean.


Most modern sources of drinking water come from surface water that flows into rivers, streams, lakes, and groundwater from wells and boreholes. That leaves 60 per cent of total precipitation to evaporate, transpire through plants, and to wet the soil. Or for people to harvest.

The Downside of Rainwater

Let’s look at some of the disadvantages of rainwater harvesting:

Supplies can be contaminated by bird and animal droppings on the catchment surfaces and guttering structures unless they are cleaned or flushed before use.

Poorly constructed water tanks or containers can suffer from leakage, algal growth, and invasion by insects, lizards, and rodents. They can act as a breeding ground for disease vectors if they are not properly maintained. All of that implies a high level of responsibility for maintenance.

How Much Water can be Collected?

The run-off from a roof is directly proportional to rainfall and the horizontal area of the roof. For every millimeter of rain, a square meter will yield one liter of water, in theory.

Expect to be able to capture only 80 per cent of what hits the roof after losses from splashing, spillage, wind, evaporation, leakage, and overflow. Build guttering and down-pipes large enough to capture peak volume run-off during intense storms.

What is the Best Kind of Rainwater Storage Tank?

Storage solutions such as rain barrels are usually about 90 per cent of total system cost. It can range from small containers made for other purposes—oil drums, food cans, etc.—up to large tanks at ground level, or sometimes beneath it. Big tanks of concrete or ferro-cement are used as storage for schools, clinics, or other institutions with large areas of roof.

In some parts of Africa, a group called Water Aid is teaching people better ways to create large village or neighborhood storage tanks of local materials or a mix of cement and sand, reinforced with wood or fencing wire.

Corrugated galvanized or safe PVC, large-diameter drainpipe is ideal as a ground-level tank when laid on slight slopes. Five-meter lengths of culvert pipe, 0.6 meters in diameter, is easy to locate. End caps and taps must be special-ordered. A full one holds about 1,700 liters.

In a semi-desert area, we built a water tower of beveled-edge thick cedar boards, like a very tall hot tub, with steel bands around it. Our homestead had a minimal well, but by collecting nearly all it produced and pumping into our 1,400-gallon wood tank, we always had plenty for home and garden use.

Consider your needs and study your options. If you need more, better, or cheaper water, consider harvesting the rain and storing it for dry periods of the year.


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Written by Barbara H. Shaw

Profile Picture of Barbara H. Shaw

Barbara Shaw gardens, writes, and makes junk art in Oregon. She earned degrees in zoology, physiology, and journalism, and writes about science, health, growing things, and energy management. She also delights in reading, cooking, photography, eco-travel and has visited 60 countries. Married to a sports journalist, she embraces being a grandmother.

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