Sorry this is a real digression on on your thread Frances but it is interesting ...
Basic background on household water systems from layperson's point of view (I only know about this because I investigated having my system changed but it was too expensive to be worthwhile).
There are two types of domestic water systems - indirect water systems and direct water systems. Indirect is a mains-fed, stored-water system that supplies the drinking water then runs into a water tank in the loft which feeds all other water outlets. Direct is also a mains-fed system but it feeds all the taps with mains water pressure and provides drinking water from any cold-water tap in the house.
A direct system is handy as it means no cold water storage tanks and drinking water in the bathroom. A direct water system is cheaper to install than the indirect system in new-build but you need good (strong) mains water pressure.
An indirect stored-water system is apparently still the most common household system.
(So indirect systems are probably old or because of poor local water pressure I think, considering they are more expensive to install, not necessarily dodgy plumbers Jay
)
I would think that as a lot of people probably still have cold water storage tanks we should probably remember to ask people where they are taking their water change water from more often
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