I recommend determining the source of the water. Roof, hardscaping, yard drainage, water table.

Have you had any contractors on site? Who told you it was due to hydrostatic pressure?

The floor guy. Is there anyway to know if it was caused by something else? There was also mold and mildew on the cement.

Did the floor guy do any testing? Have you seen the reports, can you post the info.

Did the floor guy identify the source of the water.

Maybe you need a specialty contractor vs the floor guy.

Thank you so much for the info! No, the floor guy did not do testing. Where do you think I could find a specialty contractor?

Basement Waterproofing Contractor.

Your issues could be caused by landscaping or roof drainage or?

Are you in a large population area?

Do you have a sump pump? Does it run a lot? Agree with above. You have to do everything you can to force water away from your house on all sides and go somewhere else. Grading, downspouts, french drains, hardscape, etc. If that doesn't work you may need a contractor. I helped an old house I had by adding a sump pump in the basement, but if water can't move to the sump below the slab it only helps so much.

The age of the slab is going to be PARAMOUNT to understanding what is going on. Slabs poured BEFORE the late-80's may not have plastic sheeting underneath it. Slabs from the 70's and earlier DEFINITELY do not have the plastic.

Concrete is POROUS. It is a RIGID sponge. It LOVES to grab water from the bottom and syphon it to the top and allow it to release into the home. This usually does NOT cause issues UNLESS you 'cap' it with something like solid flooring. Now the water has nowhere to go but sit underneath the vinyl. That's when you find out you have hydrostatic pressure.

Everyone above is correct. Water comes from many places and can make things WORSE. But the basics have to be there. You have to have a concrete slab SITTING on top of wet ground. Those two things HAVE to be there.

How the water GETS there...that's an exterior grading problem that can be dealt with in many ways. But it won't solve the ORIGINAL issue: a bare concrete slab touching raw earth.

Since your slab already exists, you won't be putting down plastic sheeting BEFORE you pour your slab. That ship has sailed.

What CAN be done is a "wet basement" specialist in your area can come in, do the testing (in-dwelling probes). They then come up with a plan to seal the slab. This is NOT throwing down some garage paint and going home. It is much more complicated then that.

Traditionally they shot blast the slab (an aggressive version of sand blasting...but with metal shot instead of sand). Then the raw freshly blasted concrete has 2 coats of spray-on sealant applied. It is allowed to dry/cure. Then a primer is put down and then new concrete/topping is added (and that's when you get your slab flattened nicely) and allowed to cure.

NOW you have the sealed concrete you want. But this only works if the issue does NOT exist in the slab walls. If it does, the sealant needs to be coated UP the concrete walls as well. Which can mean you have to take down any finishing already there.

Once the slab is sealed and the walls of the basement are sealed, then you can move to the exterior issues such as drainage, etc.

Considering the drywall has mould on it, perhaps it is time to open things up and find out how extensive the problem is. Because once you find mouldy drywall, you will not want to leave it there. Not for long at any rate.

Start with a local damp basement specialist. Get some estimates. And while you wait, you will want to speak with your bank to find out how much credit you have access to.