DIY tactics of unclogging your drain including pouring harsh chemicals and drain snaking with wire hangers have negative consequences. The relief they provide is temporary because you do not know what is blocking the drain.
Finding a water leak depends on whether you can see the signs. They include unexplained dampness, increased water bills, hearing pouring water without any faucet running, loss of water pressure, and greener grass in one side of your yard. To find hidden water leaks, you need to hire a professional plumber.