my ford transit is losing water and is going in the engine?

i have a 2001 ford transit duratorq 2.5.
i have had it rebuilt 3 times, the first time we changed the head gasket and water was still getting in, the second time i bought a second hand bottom end, thinking my old one was cracked and it still lost water, so now i bought a brand new cylinder head fitted it today and was driving home and 20mins later the same problem,it was losin water. please can somebody help me i have run out of solutions