I think Steve is looking for a simple water heater rather than the boiling tap water ones.
I've fitted them in places such as village halls where they only need hot water in the kitchen.
There are two main types. Wall-hung (over-sink), and under-sink multipoint ones.
Above the sink they tend to be around 3kw. Ideal for rinsing cups and filling a bowl.
Under-sink can be up around 9kw and can actually serve more than one tap if needed (multi-point.)
Easy to fit and work very well. The 3kw can use any nearby socket circuit, but 9kw needs a dedicated feed direct from the consumer unit (much like a shower unit.)
Have a look here Steve.........................
(There are three pages of them to check out.)
https://www.screwfix.com/c/heating-plumbing/water-heaters/cat830974#category=cat830974&page_size=20&page_start=0