"Cicero" wrote

Isn't there a danger that the water will become stagnant? What do you use
the water for - toilet flushing or washbasin?

Cic.

Stored water loft tanks has been used in the past for:

Feeding indirect hot water cylinder
Showers - to provide balanced pressure for hot water from above source
Toilet cisterns - to provide buffer for loss of mains water
Bath cold feed (not sure why)

This was the basis for the original plumbing in my 1970s house.

Phil