Me and you both Dave,
Some times builders will build a house and aim for a certain level in the "Code for Sustainable Homes", which is a rating system used to encourage things like recycled water. However, as I said such things are expensive so they are usually only used in high spec builds, self builds, etc. The mass market house builders want to be cheap, (Tescos not Harrods), so they don't bother with Code.
Building Regs are meant to be changing again soon, as they do regularly, raising the standards on these issues, but the Govt. are going through a consultation as they are unsure what to do about the changes. On one hand they want to raise the standards, but on the other hand, they don't want to stifle the already weak building / housing market.