If P is population of a city in thousands and Q is fire demand in litres per minute, for proper estimate of water, the Empirical formula Q = 1135 [(P/5) + 10] is suggested by

Water Supply Engineering is a branch of engineering concerned with the development of sources of supply, transmission, distribution, and treatment of water.

The term is commonly used for municipal (city) water works, but applies also to water systems for industry, irrigation, wastewater reuse, and other purposes.