Water Mains Replacement to increase flow rate

A typical shower requires 9/lpm. You have 15/lpm incoming mains water pressure, so divide 15/lpm into 2 = 7.5/lpm this in theory is what can be achieved when both showers are running simultaneously. Current legislation states that your water provider has a legal obligation to provide you with a minimum of 1bar (15psi) this generally translates to no more than 9/lpm +/-1.3 bar. If you upgrade the existing lead mains to MDPE this may increase the flow rate but not necessarily the pressure! Recommend you fit a breaker tank with with a suitably sized booster pump. See link below for illustrated purposes only: http://www.fluidwater.co.uk/tank-mounted-booster-set.php or http://uk.grundfos.com/products/find-product/home-booster.html#brochures

before you put in a combi boiler or unvented cylinder you should check mains pressure and volume,but only at a time of high usage 6am/9am,4pm/9pm to get a true reading of what your main can supply.check with your waterboard regarding what incoming pressure they can supply,if you change lead main to a larger mdpe main you will increase volume,but this may be dependent on your waterboard increasing the size of their side of the supply pipework.