On a RNoAF Sea King they had a similar water boiler to that fitted to Nimrod and Shackleton with two extra features. The water level had a barber's pole sight glass and a simmer function.
On bugs in the water tank, that was the reason Shacks had jerry cans and a hand pump. After I asked why they didn't clean the tanks - they did. I don't recall any issues on the Nimrod.