My home is a tri-level with the basement being just a few feet below grade. I am remodeling a bathroom in the basement. Once I gutted the room and removed the existing tub, I found a plywood floor on 2x8 joists. The rest of the basement has a concrete slab. Below the joists in the bathroom, I see water. I haven't yet removed the plywood to figure out what (if anything) is supporting the joists. The PVC tub drain seems loose to me so there may be a leak in a pipe. The water could also be ground water. I don't have any odor so maybe the pond of water is acting as a giant trap.
How do I proceed? Should all the lumber be removed, correct the PVC drain pipe, and then pour concrete in the space? The room is about a 7' cube. The house was built in 1962, but the bathroom was added later. I plan to hire professionals for the plumbing and a new floor but I want to understand what I am asking them to do. I want to replace any galvanized or cast iron pipe with PVC.
The supply lines are under the floor submersed in the water. The wall where the sink and toilet will be located are cement block the first 24". Instead of routing new copper under the floor, I am thinking of using PEX routed through the ceiling. Will PEX fit behind the drywall with 1/2" furring strips between the drywall and the block wall?