So far, how much water have you topped up? You may want to check your engine oil for water contamination. Can use the dipstick and engine oil filler cover to check for sludge or milky stuff. The missing coolant could be leaking into your engine.

Start your car with aircon switched off and let it warm up. Open bonnet and observe for any water dripping.

May I also suggest changing the radiator cap first, before touching the radiator hoses? Meanwhile, do check the engine oil appearance regularly.