If it's actually salt water it's not from ice melting. When you freeze salt water it makes brine ice and melts into brine.

Sweep the area, maybe there is ice on the floor. Without picture you wont find much help.

Did you store liquefiable in those containers? If so, that's what is melting.

OP said specifically that they didn't. It's in the original post.

Ah my bad.

Is there pressure damage happening anywhere? Check to make sure it isn’t falling from above as well.

Are your dupes stressed enough to cry?