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Regulation 5 of the Water Supply (Water Fittings) Regulations 1999 sets out the works for which a person must give notice to the water undertaker before beginning, and the installation of a garden watering system is on that list, alongside items such as pumps, water treatment units, pressure-reducing valves and certain baths and bidets. The construction of a pond or swimming pool with a capacity greater than 10,000 litres which is designed to be replenished by automatic means is also notifiable. The procedure is straightforward: give notice of the proposed work, obtain the undertaker's written consent, which is not to be unreasonably withheld, and comply with any conditions attached to it. If the undertaker does not respond within ten working days, consent is deemed to have been granted unconditionally.

There is a practical reason to care beyond compliance. Certain fittings installed by an approved contractor do not require prior notification, which is why installers who are part of an approved contractor scheme make a point of saying so. Ask an irrigation installer directly whether they will be notifying your water company or whether they work as an approved contractor, and get the answer in writing. A homeowner who has a system plumbed in by someone who has never heard of regulation 5 is the one left dealing with the water company later.

The risk that the water fittings regulations are most concerned with in a garden is water flowing the wrong way. Schedule 2 to the Water Supply (Water Fittings) Regulations 1999 requires that every water system shall contain an adequate device or devices for preventing backflow of fluid from any appliance, fitting or process, and that no supply or distributing pipe shall convey, or be connected so that it can convey, fluid in the categories that are not wholesome water. A drip line sitting in soil that has been fed and treated, a hose end submerged in a pond or a water butt, or a sprinkler head lying in a puddle, are all situations where a drop in mains pressure could pull garden water back towards the house.

In practice this is why an outside tap and a garden system are fitted with the appropriate backflow protection rather than simply teed off a convenient pipe, and why the type of protection depends on what the water could be contaminated by. It is not a detail to negotiate down in a quotation. If a quote for an irrigation system makes no mention of backflow prevention or of notifying the water company, that tells you something about the installer, and it is worth asking the question before comparing prices.

Under section 76 of the Water Industry Act 1991, a water company that thinks it is experiencing, or may experience, a serious shortage of water for distribution may prohibit specified uses. The list in the Act includes watering a garden using a hosepipe, cleaning a private motor vehicle using a hosepipe, filling a domestic swimming or paddling pool, drawing water by hosepipe for domestic recreational use, maintaining ornamental fountains and cleaning walls, windows, paths or patios with a hosepipe. A prohibition must specify the date it takes effect and the area it applies to, and breach is an offence punishable on summary conviction by a fine up to level 3 on the standard scale. The company must also make arrangements for a reasonable reduction of charges for the prohibited uses.

The Water Use (Temporary Bans) Order 2010 supplies the definitions that decide whether your particular set-up is caught. Using a hosepipe includes drawing water through a hosepipe from a container and applying it, and filling or partly filling a container by hosepipe and then applying the water. A garden is defined broadly and includes lawns, grass verges, allotment gardens and other green spaces, but it excludes land used commercially for growing crops or plants, plants grown for sale, National Plant Collections, temporary garden or flower displays, and plants in pots outdoors or under cover such as in a greenhouse. There is an exception where the use is for health or safety reasons. Because each company publishes its own notice and its own concessions, read the notice rather than relying on what a neighbouring company has announced.

Most British garden systems run on mains water because it is simple and always available, but it is metered in many homes, it is the supply a temporary use ban restricts, and it is the one that brings the water fittings regulations into play. Stored rainwater is the obvious alternative for a garden: butts and larger tanks fed from roofs cost nothing to fill, the water suits most plants, and a small pump feeds drip lines perfectly well. The limits are volume and reliability, since a dry spell empties the store exactly when the garden needs it most, so most households end up with rainwater as the first source and a mains connection as backup.

Taking water from a borehole, a well, a stream or a pond is a different matter and belongs to abstraction law rather than plumbing. Section 27 of the Water Resources Act 1991 exempts the abstraction of a quantity of water not exceeding twenty cubic metres in any period of twenty-four hours, provided it is not part of a continuous or serial operation exceeding that amount. A domestic garden rarely approaches that figure, but if you are considering a borehole it is worth confirming the position with the Environment Agency before drilling, and remembering that a private supply brought into the house raises separate questions that your local authority deals with.

A proper survey looks at pressure and flow at the tap before anything is designed, because those two figures determine how many emitters or heads can run at once and therefore how many zones the garden needs. The installer should also look at where the supply will be taken from, how the backflow protection will be arranged, whether notice to the water company is required, where the controller will live and how the pipe runs will avoid existing services, tree roots and the areas you intend to dig later.

Installation then runs from the connection outwards: the supply point and its protection, a filter and any pressure regulation, the main run, the zone valves, then the distribution pipe and the emitters or heads, which are best positioned with the planting in mind rather than in a grid. At handover you should be shown how to change the programme, how to shut the system down, how to flush the filter and what to do before the first frost. Ask for a simple plan of where the buried pipe runs, which is the document you will want the first time you dig a new bed.

If you want to compare installers, LokalMatch takes the details once: the size and layout of the garden, which areas need watering, whether there is an outside tap or a water butt to work from, and whether you want pots, beds, a greenhouse or the lawn covered. Matched irrigation contractors covering your postcode then contact you. The contractors pay for the requests they receive, while LokalMatch does not install systems, does not set prices and does not vet, rank or recommend anyone, so ask each one about backflow protection, water company notification and how many zones your pressure will actually support.