We recently had a distinct lack of mains water round here for a few days.
We were lucky in that our supply didn’t stop, it just reduced to a (normal pressure) dribble (mains fed toilet cisterns and loft cold tank filled slowly).
Others weren’t so fortunate and got none, including many new builds which had no cold tank.
I imagine the smaller new builds would have a combi.
What would larger new builds be likely to have?
A high pressure hot water tank heated from a sealed system gas central heating system?