Please find enclosed Schematic Drawing for a Residential Combined Water Meter and Fire Protection. What is the best way to determine what size of pipe from water main is needed to building. From my experience the best way to determine water pressure is to go to the nearest two hydrants and flow them with a pito gauge. Problem being it depends how far the main is away from the source as this causes just as much friction loss in pressure as elbows and tees. In Industrial and commercial applications we have a six inch feed to operate with and from the pressures from this size we hydraulically calculate our pipe sizes. for the building being applied for. Does any one know what the lowest pressure we could have to accommodate a 3/4 inch line which is not compatible to 1" Blaze Master. I would prefer a 1" line and not have to install copper with nominal sizes of 3/4 inch with nice friction loss numbers. and low K-Factor Sprinkler heads listed for residential services very expensive.