Water quality and filtration

Rainwater arrives clean from the clouds, then picks up whatever sits on your roof: moss fragments, bird droppings, lichen dust, pollen, airborne particulates. For ornamental and edible crops this is harmless — a light turbidity and the occasional floating leaf do not trouble a courgette or a dahlia. What you must exclude are large debris (which clogs taps), stagnant pools (which breed mosquitoes), and contamination from treated timber, asbestos or bitumen roofs (which can leach toxins).

The first line of defence is a gutter guard or leaf mesh along the roofline, stopping most organic matter before it enters the downpipe. The second is a first-flush diverter, which discards the initial 20–30 litres of each rainfall event — the dirtiest fraction that washes the roof clean. After that, a simple mesh filter (1–2mm holes) over the butt inlet catches the rest. This three-stage approach keeps your water clear enough to drink if you were desperate, though we do not recommend that without proper treatment.

For precision growers — hydroponics, microgreens, seedlings in sterile compost — add a 5-micron sediment filter (£10–20) in-line before your watering system. Change the cartridge every 6–12 months depending on use. If you are watering edibles that grow at soil level (lettuce, strawberries, salad leaves), avoid watering directly onto foliage in the final two weeks before harvest. Root crops and fruiting plants (tomatoes, beans, apples) have no such concern — rainwater can go anywhere.