Oceans may be a problem, but smaller saline pools shouldn't be.
Saline pools would have multiple benefits. Not only when kept warm could you use them to generate oxygen with phytoplankton, if you have to cut off power for some reason, they'll work as a great thermal heatsink, and they will not freeze as fast so they present less risk of piping damage.
Also, humans who come along are not going to be sterile. Seawater is friendly to a lot of different organisms. Any open system is going to be full of goo pretty quick.
Saline pools would have multiple benefits. Not only when kept warm could you use them to generate oxygen with phytoplankton, if you have to cut off power for some reason, they'll work as a great thermal heatsink, and they will not freeze as fast so they present less risk of piping damage.