Garden irrigation

Garden watering is lightly regulated, but two areas bite: protecting the mains from backflow (a legal duty) and temporary bans during drought.

• Any connection to the mains for irrigation must prevent backflow under the Water Supply (Water Fittings) Regulations 1999. A garden tap/system is a Fluid Category 3 (or 5 for fertigation) risk — fit a double-check valve, and notify your water company before installing fertigation. ^[1][2]
• During a Temporary Use Ban (hosepipe ban) you cannot use a hosepipe or automatic sprinkler for gardens. Drip/trickle irrigation connected to the mains is also restricted, but a watering can, or a system fed from a water butt / stored rainwater, is normally exempt. ^[3][4]
• Rainwater harvesting for the garden needs no permission, but stored rainwater must never cross-connect to the mains without a Category 5 air gap (type AA/AB) — it is a contamination risk. ^[1][2]
• Metered vs unmetered supply changes the economics, not the law: on a meter, every litre saved by drip over sprinkler shows on the bill, so SuDS-style efficiency pays back faster. ^[4]
• Outdoor electrics for pumps, timers or solenoids must comply with BS 7671 and Part P — RCD protection (30 mA) is mandatory and notifiable work should be done or certified by a registered electrician. ^[6][7]

Field numbers, not marketing copy. Adjust for your soil, plants and product datasheets.

• Bucket test sets your budget: time how long the outside tap takes to fill a 10 L bucket. 20 s = 30 LPM; 30 s = 20 LPM. The system can never demand more than this, so flow — not pressure — usually decides how many zones you need.
• Water early morning (04:00–08:00). Midday loses ~30% to evaporation; cool pre-dawn hours lose ~5%, and foliage dries before nightfall so you avoid fungal disease.
• Deep and infrequent beats shallow and frequent: longer runs every few days drive roots down and build drought resilience; daily sips keep roots shallow.
• Group plants by water need (hydrozones) and put each on its own zone — never mix thirsty veg with drought-tolerant shrubs on one valve.
• Mulch 50–75 mm over drip-line: cuts surface evaporation, suppresses weeds and protects the tube from UV.
• Pick the method to the planting: drip-line for beds & hedging, gear-driven pop-up rotors for large lawns, micro-drip spaghetti for pots & patios.
• Friction loss is real — every 15 m of 13 mm main run and each fitting drops working pressure. Keep laterals under ~30 m and split into zones rather than starving the far end.
• Emitter spacing follows soil: sand wets a narrow, deep bulb (~30 cm spacing), clay wets wide and shallow (~50 cm). Loam sits in between (~40 cm).

The build-and-maintain checklist that keeps a system reliable past its first season.

• Bucket-test method: fill a 10 L bucket, note the seconds, then LPM = 600 ÷ seconds. Repeat twice and average — pressure dips when neighbours draw water.
• Always fit a filter (120–155 mesh) downstream of the pressure reducer — grit blocks drippers faster than anything else, and inline emitters are not field-cleanable.
• Set a pressure reducer to the dripline's rated pressure (typically 1.0–1.5 Bar). Mains at 3 Bar will blow fittings off and over-emit.
• Winterise: before first frost, isolate the supply, open the lowest drain, and blow down the laterals with low-pressure air. Trapped water splits tube and cracks valves.
• Service annually: flush laterals by opening the end caps, clean the filter, and check each solenoid actuates from the timer before the growing season.