[racer_d]

Can't be sure with such a short story. The coolant tanks are known to fail. Assuming your rear trunk (boot) was also wet, then its replacement made sense. Having replaced the tank and kept pressure where it should be, it could be that the next "weak" spot gave out.. in this case a line/fitting at the front of the car.

Had you noticed where it was leaking before the coolant tank replacement? Was it actually water instead of coolant? (ie an a/c evaporator dripping vs actual engine coolant leaking?)