engine dying 300TE

Can anyone help with the weirdest problem. My recently purchased 300TE is a stunner, but.... it has a problem where the engine simply dies. There are no prevailing conditions, and it does it under load, on the over-run, uphill, downhill, slow, fast, hot, cold, if you get the picture? It simply dies, and then fires up again and runs normal. It sometimes will stall completely, if you are going slowly, and that's scarey, (no P/S, brakes etc.) then you turn the key and it acts like there is no problem.
My local garage found water in my tank, and drained and disposed of £60 of fuel (That HURTS) but it does not seem to have made any difference. They have changed the fuel filter but it is no different. Can anyone throw any light...