2003 Pontiac Grand Am Leaking Coolant

Purchased 2003 Ponitac Grand Am GT new. Last year noticed temp raising and falling over normal 200 degree. Had the thermostat replaced. Last month had to start adding small amounts of coolant once a week after low coolant light came on. Mechanic replaced the coolant light. Did not help. While driving last week temp when to 230 degree. I shut off added water and squezzed the hose going to the thermostat. Hear a loud bang. Checked the oil and found no water. Drove care to mechanic who replaced the thermostat, pressure tested the system anc flushed the engine. Car now running at normal temp but still using about a pint of water. No leak visible. Check aroung water pump, under the car and all hoses. No water in oil. Low coolant light comes on when system is low on water. When is water going?