Brian Gaff wrote

If a carpet of the normal house kind ie not one meant for a bathroom,
which are designed to get wet, gets wet, how is the best way to dry it and
stop it from rotting?

You don’t need to do anything special after using a carpet cleaners.

May seem daft, and I know that if its polluted water from a naff central
heating leak or a flood where more than just a bit of rain is involved its
probably a throw it away job,

Not if you dry it well.

but it was just that I do have the odd accident with fluids and wondered
if simply using a fan heater on it

Yep.

or throwing it over a radiator might do the trick.

Not a great idea with a full room carpet.

I'm interested in stains and smell, in the main.

Works fine to use a proper rented industrial carpet cleaner.