poor flow rate for multiple showers

[markythesparky]

My sons house has three showers but none seem to be any good water pressure seems ok(2.5bar) but flow rate about 10ltr min but it drops off if a second tap is opened ,the house is 150mtr from the road so a long newish 25mm supply pipe from main supply ( which just to make it a bit more a problem united utilities dont know where its connected they gave up looking when the wanted to fit a meter so cant check if mains shut off is fully open) he has an unvented hot water system (Gledhill with pressure vessel) is there anything he can get fitted (water accumalater or something ) to ensure sufficient flow for a property of this size I realise it may be expensive but it needs something doing.property remodeled about 10 years ago most pipe work internal plastic 15 and 22mm.

 

[markythesparky]

Also check the meter size. Most of the time the numbskulls stick a 1/2" meter on a 2" main or whatever which means you are always throttled.

no meter