My other half has just inherited a pretty ramshackle house that's been neglected for about 20 years.
When I was nosing about the loft and airing cupboard a week or two ago prior to doing a small plumbing job, I realised that there were only two outlets from the cold water tank. One goes directly to the bathroom shower; the other goes, as far as I can tell, ONLY to the bottom of the hot water tank. That means that all the cold taps in the house (and there are six on the bath and varous sinks, not to mention the feed to the washing machine) are on the main. (I first discovered this when I couldn't drain the cold tank via the bathroom taps)
What's more, it means the two toilet cisterns are fed directly from the main.
I was always under the impression that the regulations stated that only one sink outlet should come off the mains and that toilet cisterns must be fed from stored water so that they could flush if there was an interruption to the mains.
Was I wrong, or is the plumbing in this house illegal?
It has never been a requirement that all but one cold taps have to be connected via a header tank. In fact it is quite the opposite. At least on tap must be connected to the mains for drinking water purposes as stored water is not classified as a suitable supply and nowadays, all outlets that may be used for drinking should be connected to the mains.
In the past it was a requirement that toilet cisterns be connected to a stored supply so would remain operative in the event of a supply failure. This regulation no longer applies.
It was often seen that bath cold supplies were header supplied because of the large flow required to fill a bath. With new larger mains feeds, this is no longer necessary.
By far most properties will have a plumbing arrangement as per your description which is legal and quite satisfactory.