Most of the first fix plumbing is pretty standard. We have designed the overall positioning of bathrooms to be as logical as we can from a plumbing point of view. So they are to an extent stacked one above the other on each floor, This also helps to minimise the dead legs of piping from the hot water tank to the various taps, and therefore the amount of hot water that is left in the pipes (and therefore left to go cold) when the taps are turned off.
The principal addition in this house is a heat recovery unit known as a heat squirrel: this takes the waste water from the bath and showers and runs it through a heat exchanger to pre-heat the cold water going into the hot water tank. It will be difficult to quantify the contribution this makes, but it claims to make a difference. It does need to be considered at the first fix stage so that the waste pipes from the bath and showers are plumbed into the heat exchanger rather than into the normal drains.
This is the “heat squirrel”. This is quite a large cylinder. The jacket is supplied with the warm waste water from the bath and showers, and the fresh water supply to the hot water tank passes through a heat exchange coil within the tank. Thus heat is transferred from the waste water to the fresh water. I suspect this especially comes into its own when there is a sudden demand for lots of showers/baths in quick succession.