I reckon your next step is to clean the 2 strainers in the water operation block after this i think the problem will be fixed.
first strainer is on the bottom of water pressure regulating valve - not marked and never mentioned in the manual
second y-strainer before solenoid block
we also had problem with rusty water supply pipe, there was pressure on local gauge but when solenoids opened there was not enough water and pressure would drop to almost 0 - had to put a hose from buffer tank to purifiers for testing - with open valve pressure is at least 2 bars like dieselbike mentioned
Alfa Laval purifiers have simple test to check quantity of water with a bucket....