Vauxhall Astra losing water

Just before christmas I was driving down the motorway when the heater started blowing cold air with the heating turned up, when I checked I had lost all water in engine water bottle.

Turned out a hose had split, had it replaced and all was good untill a few weeks ago when the same started hapening again. On the way back from work one day I noticed the problem again and stoped to check it out, one of the hoses had blown off. Problem then started again day later,I toped the water back up and the rediator was leaking due to a crack so got that fixed.

Now its still losing water, I top water up every morning then leave for work, it seems as long as you got your foot on accelerator it will blow warm air but as soon as you take foot off pedal you get cold air. When I get to work engine water is less than quater full, any ideas?