Make Every Drop Count – Rainwater Harvesting on Your Allotment

How Much Water Do You Need?

Water requirements vary depending on soil type, climate, and crops. For example:

• With mulching and no-dig, a typical plot might use around 2,000 litres per year.
• A plot with many leafy crops grown on open soil could use over 8,000  litres per year

To use as much collected rainwater as possible, you need sufficient storage capacity. Normally, about 80% of stored water is available for use, as some is lost to evaporation, so planning for extra capacity is essential.

Collecting Rainwater

Rainwater can be harvested from:

Storage is much easier if water is collected above ground, as gravity can feed it into barrels or containers. For polytunnels, installing timber rails about 1 metre off the ground on the inside allows square-section guttering to be attached to the outside. Silicone sealant ensures water runs straight into the gutter.

For storage, there are a few popular options:

• Plastic barrels (200 litres) – cheap, simple, and effective
• Intermediate Bulk Containers (IBCs, ~1000 litres) – offer larger capacity, but check what they previously contained and paint or shade them to prevent algae growth.

Practical setup tips:
Raise containers for easier access, interconnect them for filling, and always use lids to reduce evaporation and prevent accidents.

Typically, you can use about 80% of the collected water, as some will be lost to evaporation.

Watering Wisely

How you water can be just as important as how much you collect. Some simple tips:

Water the soil at the base of plants, under the foliage, to direct water to the roots.

Avoid watering in the middle of a sunny day; early morning or late evening watering allows roots to absorb more.

Seedlings and small pots may need light and frequent watering; using a tray to water potted seedlings works well.

Encourage established plants to develop deep roots by watering deeply once a week rather than lightly every day.

Water the soil lightly before sowing seeds to prevent slumping or capping, which can hinder germination.

Some plants, like peas and beans, may benefit from occasional periods of reduced watering. Root vegetables, like carrots and parsnips, usually need less frequent irrigation.

Make Rainwater Work for You

Collecting and using rainwater isn’t just eco-friendly—it’s practical, too. It ensures your plants get the water they prefer, reduces reliance on mains water, and can even save you money. With a few barrels, some simple drainage, and a bit of careful planning, your allotment can become more resilient through dry spells and summer heatwaves.

Every drop counts, and starting now means your garden will be ready for the months ahead. So grab a barrel, direct that runoff, and let your plants drink straight from the sky!

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