Separate submarine plumbing reduced fluid contamination

Were submarine tanks for diesel, water, and distilled battery water kept on isolated plumbing circuits?

Designers tried to keep those fluid systems isolated so their contents would not mix.

Designers tried to isolate the circuits for tanks carrying different fluids, especially where mixing could contaminate distilled water needed for batteries. This was a design intention rather than a guarantee of perfect separation on every boat. Submarine systems engineering had to control fluid purity as well as weight and trim.