If you are confident with plumbing you can do some of this yourself. Two parts of the job catch people out, and both are expensive to put right.
The electrical supply
The tank needs a 13 amp socket in the cupboard under the sink. If one is already there and in good order, you are fine.
If there is not one, have a qualified electrician add it. In England and Wales a brand new circuit is notifiable work under Part P of the Building Regulations, so it has to be done by a registered electrician or signed off by building control, and the certificate is something a future buyer will ask to see.
The hole in the worktop
The tap needs a 35mm hole. In a stainless steel sink that is straightforward. In granite, quartz or any stone worktop it needs a wet diamond drill and a steady hand, and a dry drill or the wrong bit chips the surface or cracks the slab. A cracked worktop costs far more than the tap.
If you are replacing an existing tap we normally use the hole that is already there, which avoids the problem completely.
The water side
The work has to meet the Water Supply (Water Fittings) Regulations 1999, which cover things like backflow and the pressure the tap needs. Most 4 in 1 taps also carry normal hot and cold water, so they connect to both supplies under the sink at the right pressure.
Your guarantee
Most makers tie the tap's guarantee to it being installed correctly, and some ask for proof before they will cover a fault. Read your own tap's manual before you start, because that is the document the maker will hold you to.
If you have already started
We service and repair taps we did not fit, so if something is not right we can pick it up. Send a photo of the open cupboard under your sink with your enquiry and we will tell you what we are looking at.
If you would rather we did it
We fit any major brand for a fixed £240 including VAT, whether you bought the tap from us or already have one. That covers connecting the tap, setting up the tank and filter, checking every flow for leaks, and showing you how the safety controls work before we go.