A plumber is inspecting a residential water service with a 25 mm copper pipe. The pressure gauge at the main entrance reads 450 kPa, and a flow test at an outdoor hose bib indicates a flow rate of 0.8 L/s. If the house has multiple fixtures that can operate simultaneously, leading to an estimated peak demand of 1.5 L/s, what would be the approximate pressure at a fixture on the second floor (6 meters above the main entrance) during peak demand, assuming an additional 70 kPa pressure loss from fittings and internal piping?

Question: A plumber is inspecting a residential water service with a 25 mm copper pipe. The pressure gauge at the main entrance reads 450 kPa, and a flow test at an outdoor hose bib indicates a flow rate of 0.8 L/s. If the house has multiple fixtures that can operate simultaneously, leading to an estimated peak demand of 1.5 L/s, what would be the approximate pressure at a fixture on the second floor (6 meters above the main entrance) during peak demand, assuming an additional 70 kPa pressure loss from fittings and internal piping?

Answer options: ✅ 280 kPa

• 200 kPa
• 350 kPa
• 150 kPa

Correct answer: 280 kPa

Explanation: To calculate the pressure at the fixture, start with the main entrance pressure (450 kPa), subtract the static head loss due to elevation (6 m * 9.81 kPa/m ≈ 59 kPa), subtract the pressure loss from fittings and internal piping (70 kPa), and then estimate the pressure loss in the main service line at peak demand. For a 25 mm copper pipe at 1.5 L/s, the friction loss would be significant, but even without exact calculations, the other losses bring the pressure down considerably. 450 kPa - 59 kPa - 70 kPa = 321 kPa. Considering additional friction loss in the main service at peak flow, 280 kPa is the most reasonable estimate.