How do I get power and water to a greenhouse?

These two services get treated as one job and they are completely different. Water is a Saturday morning with a hacksaw. Electricity is regulated work with real consequences for getting it wrong, and it is also the one that transforms what a greenhouse can do — heat, propagation, lighting and automatic watering all depend on it.

Safety

Step by step

1. Start with the water, because it is easy.Fit gutters along both eaves if the greenhouse does not have them, run a downpipe into a water butt beside the door, and put the butt on a stand high enough to get a can under the tap. A greenhouse roof collects a surprising amount.
2. Size the storage realistically.One standard butt fills quickly and empties quickly in July. Two or more linked with a connector kit, or one large tank, is what carries a greenhouse through a dry spell. Link them at the bottom so they fill and draw evenly.
3. Keep the collected water clean.A leaf guard at the gutter outlet, a lid on the butt, and siting the butt out of direct sun. Warm, sunlit, debris-filled water goes green and smells, and it can carry damping-off organisms to seedlings.
4. Use rainwater for the plants and tap water for seedlings.Rainwater suits almost everything and is essential for ericaceous plants in hard-water areas. For seed sowing and very young seedlings, mains water is the safer choice because stored rainwater can carry pathogens.
5. Consider a mains standpipe only if you genuinely need it.A garden tap extended to the greenhouse makes automatic irrigation possible. It must be installed with a suitable backflow prevention arrangement to protect the mains supply, which is a regulated requirement — a plumber will know the current rules.
6. Treat electricity as a professional job from the start.A greenhouse supply means a dedicated circuit from the consumer unit, steel-wire-armoured cable buried at a proper depth or run in conduit, correct earthing for an outbuilding, RCD protection, and a small consumer unit in the greenhouse. It is notifiable work and it comes with a certificate.
7. Specify what you want before the electrician arrives.Number and position of sockets, whether you want lighting, whether a heater will draw a significant load, and whether you want a supply to a shed on the same run. Getting this right at design stage is far cheaper than adding to it later.
8. Use the temporary option correctly, if at all.An outdoor-rated extension lead, fully unwound, plugged into an RCD-protected socket, used while you are present and brought in afterwards. Never for a heater, never left out overnight, and never in the rain.

Tips

• Ask the electrician to include one more socket than you think you need and to allow capacity for a heater. Adding load to an undersized supply later means doing the work twice.
• A battery or solar-powered irrigation timer on a water butt gives you automatic watering with no mains supply at all, and is the cheapest way to solve the holiday problem.
• Gravity from a water butt gives very low pressure. Most drip systems need either a header height of a metre or more, or a small pump.

Common mistakes

• Running a permanent extension lead down the garden — It is a trip hazard, it degrades in UV, connections corrode, and a high-current appliance on a coiled lead overheats. It is the most common serious electrical hazard in a garden.
• Burying ordinary flex or twin and earth cable — Buried supplies need steel-wire-armoured cable at a specified depth with marker tape, or protected conduit. Anything else will eventually be cut by a spade.
• Connecting a greenhouse tap without backflow protection — It creates a route for contaminated water to be drawn back into the mains, which is why the requirement exists. A plumber will fit the correct arrangement.

Questions people ask