I absolutely agree with you about being careful. That's why I gave comparison figures. We have a high Rateable Value - not the same as Council Tax banding.
Apparently the Rateable Values were set in the 1970s, as a guideline for the amount of rent which landlords could charge on a property. These guidelines are now out of date for rent, but water companies still use them to calculate water bills where there is no meter. My Dad lives alone now, but he's paying the same amount as though the family were still there. Also, it makes no difference if he is on holiday or at home, the bill is the same. But he's old, and unwilling to make changes.
What you have to do is face the enemy - get hold of the facts and try to work out if you would make a saving or not.
Using a water butt helps in the garden.