Overheating

Drove car for five hours and when at destination over the four days used air conditioning a lot as days were warm, then drove five hours back on fourth day. When nearly at destination heard a warning beep and temperature gauge had maxed out to 130. On opening bonnet the water coolant container was boiling/steaming over. I then left it twenty minutes to cool down and then opened up the coolant container which was not its usual tight lid and no pressure at all. Coolant/water was completely empty. I then refilled with water and drove back home which was approx fifteen miles (thirty minutes) without any issues. Now I do not know what to do as we have a journey in twenty four hours which will be nearly two hours of driving and do not know if this was just a low coolant problem or something more serious! Is there anyway of identifying what could have caused this? The air conditioning/heating unit has never been as powerful as our same model previous galaxy and yet is quite noisy. Also the engine idle is incredibly noisy. Like a large cat/lion purring. Could these things be related? Many thanks for your help.