Floor leak

The floor in my lobby/bathroom has lump in it. I know there is a pipe under there that feeds the shower and sink as last year the floor came up in a certain area where there was an elbow joint and thought it was fixed this lump is further along. Although I say all this there was no definate leak but the ground was gritty/ sandy. Is there a device which shows leaks etc without digging everything up plus would this be a plumber job or builder type