What psi/ft gradient is used for fresh water?

• A. 0.433 psi/ft
• B. 0.465 psi/ft
• C. 0.5 psi/ft
• D. 0.4 psi/ft

Answer: (A)

Fresh water pressure rises with depth at a rate set by the fluid’s weight density. In imperial units, the pressure increase per foot is found from p = γh, where γ is the weight density. Fresh water has a weight density of about 62.4 lb/ft^3. Converting to psi per foot: 62.4 lb/ft^2 equals 62.4/144 psi, which is approximately 0.433 psi per foot. So the standard freshwater psi per foot gradient is 0.433. This value is used in practice for calculating hydrostatic pressure in clean water systems; seawater is a bit heavier, around 0.445 psi/ft, but for freshwater that 0.433 psi/ft is the reference.