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I've learnt a hell of a lot from this forum over the last year or so and I'm so grateful to everyone for their help. On pipe diameters, I THINK, the following is best practice for selecting HW pipe diameters to come off a secondary loop, but just wanted to double check before I go ahead with it: showers 15mm hand basins 10mm baths, can be 15mm unless bath tub is super big and you have a high flow bath filler in which case case 22mm till fill the super bath more quickly My remaining questions are set out below (for context, we will have a UVC with about 3 bar of pressure and relatively good flow rate, although don't know what yet as Thames Water haven't done the upgrade yet; we currently have about 18L/min and they promised me something silly like 70 litres a minute, but I asked them to put it in writing and they refused, so I'm guessing it will be less than that): Does the same rule about hand basins apply to kitchen sinks? Any reason why 10mm might not be enough in the kitchen. Looking at my kitchen tap, it has very narrow 9mm hoses, so I can't see why anything bigger than 10mm would be worthwhile. It would just increase the dead leg that needs to be cleared each time it's used, but thought I'd better double check. what happens to an outlet further down the secondary loop when one opens the bath filler (which is rated at 33L/min) that is served by the 22mm secondary loop? Would the majority of the water in the secondary loop go to the bath meaning another outlet further along the secondary loop (i.e. further away from the UVC) that is trying to compete with the bath filler would really struggle, or would a fairly decent flow rate of say 25L/per minute, together with the 3 bar pressure from the UVC ensure that dynamic pressure is sufficient that the other outlet is still usable. should cold water pipes feeding each of these outlets always match the diameter of the HW pipe feeding them?