What is the primary power source for the potable/wash water system (PWS)?

• A. Bleed air regulated to 30 psi.
• B. Electrical power from the AC bus
• C. Hydraulic pressure from the system
• D. Battery power only

Answer: (A)

Potable and wash water is pressurized by a bleed-air driven pump that uses engine bleed air regulated to about 30 psi. This setup provides a steady, reliable pressure source for the water system, independent of the aircraft’s electrical status. The regulator keeps the pressure at roughly 30 psi, ensuring safe, consistent flow to taps and wash outlets without overpressurizing the lines.

Using bleed air as the primary source makes the system robust: it’s available whenever engines or the APU are supplying bleed, and it avoids heavy reliance on electrical power. Electrical or battery-only options would depend on the aircraft’s electrical systems and could be less dependable in certain failure conditions, and hydraulic pressure isn’t suitable for potable water due to contamination risks.