hi all. needing a bit of help please. I do new build properties and have a customer that will not accept a loss of flow rate when using multiple outlets, eg taps restricted flow rate 6 l/min is achieved but reduces to 5 l/min when using two outlets. what i need is the british standard and /or nhbc standards that set out regulation for using multipe outlets. any ideas ?. this is on a sn unvented santon plus instalation