Any professional builder/ handyman plumber should be able to find the cause, get someone in quickly they will have to do some minor damage to find the problem

Good luck

Water doesn't run uphill so it will be a leak somewhere in the kitchen running down a pipe...plumber required.

I would instruct a leak detection company to attend with specialist equipment like thermal imagining equipment and damp readers to pin point the leak then instruct them the carryout the trace and access to find the leak. Obtain a report from the attending trace and access engineer and then instruct your insurance company and also send the report to them. The cost of the leak section and any repair work that needs carrying out will be covered under your home insurance company.

It is likely to be one of three things, either mains water, central heating water or a drainage pipe. If water is coming out continuously and your toilets are working fine it's most likely a burst water pipe and will probably need the section of concrete floor digging up if there is no option of rerouting a new pipe.
If you think the drains may be under this section of floor or you have noticed the toilets are not draining away as they should a drain engineer would be able to do a CCTV of the internal condition of the drain and tell you if there is a problem.