The other thing I forgot to add is that some water also contains heavy
metals that can also be neutralised by the addition of a water
conditioner....When chosing a water conditioner it is good to check that
it has chlorine, chloramines and heavy metals covered - not all do (or
so I've heard) - a lot of conditioners also contain other stuff which
claim to benefit/promote fish health - don't know if they do or not....

Gill