Steel pipe is generally used aboveground for firewater lines. Underground piping systems can be constructed of steel, cement-lined steel, or high-density polyethylene (HDPE). Concrete is sometimes used but is seldom economical except in large diameters. HDPE does not corrode, resists accumulation of scale, and is very ductile and lightweight. But, because it fails when heated, it can only be used in buried installations, where it is also protected from mechanical damage and radiant heat.
High-performance butterfly valves and gate valves are recommended for block valves in firewater distribution systems. They should provide reasonably tight shutoff and use sealing materials that do not swell or deteriorate with age. Any valve that may be buried, and that may therefore not receive frequent maintenance, should be very durable.