Water Supply Systems Practice Questions

Water supply questions divide into two halves that are graded very differently. The sizing half is arithmetic you can check: available pressure in, friction and elevation losses out, required pressure at the fixture left over. The protection half (backflow, cross-connection control, thermal expansion) is almost entirely recall, and it is where exams concentrate their hardest questions because the consequences of getting it wrong in the field are contamination rather than inconvenience.

On the sizing side, work the pressure budget in a fixed order and the questions stop being ambiguous: start from the supply pressure, subtract the pressure regulator loss if there is one, subtract 0.433 psi for every foot the water has to rise, subtract meter and friction losses, then compare what is left against the minimum flow pressure the fixture needs. Exams set the numbers so that one term is the one that breaks the budget, and the question is really asking which one.

On the protection side, learn the hierarchy by hazard rather than by device name. A reduced-pressure principle assembly is the answer when a health hazard is present and the connection is continuous; a double check assembly covers non-health hazards; an atmospheric vacuum breaker only works downstream of the last valve and only against back-siphonage; an air gap is the one protection that cannot fail because it is a physical separation, which is why it is required at an indirect waste receptor. A question that names the contaminant is telling you which tier of protection it wants.

Thermal expansion rounds the section out. A closed system (one with a check valve, backflow preventer or pressure regulator between the main and the water heater) has nowhere to put the volume that heating creates, so an expansion tank becomes necessary. Where the main pressure exceeds 80 psi a regulator is required, and installing that regulator is itself what closes the system.