People mention to me all the time how well their hair behaves in London - last time someone said it was a lady in a shoestore in Toronto who said how much she missed her London locks (well, not quite like that...). The hardness in the water here seems to stop hair from getting too fluffy
I knew an English girl who's hair initially fell out on moving to San Francisco, but my family has hosted loads of people from Spain and other parts of the world where the water is softer and none have experienced major hair loss. My husband moved here permanently from Japan last year and there was no hairloss from him either.
Has your diet changed at all? Again, have you tried switching brands to a UK formulation? And all those jokes about beer aren't completely stupid - it's extremely good for your hair applied topically.
If it is due to tolerance (I tend to get an upset stomach for a while when I drink tap water in another part of the world so I don't see why the water wouldn't affect the colony of bacteria that lives in the sebum on your head) I'm not sure that putting off getting acclimatised by using spring water will be beneficial in the long run. Main reason for concern is that it is unlikely that you will fully rinse all the shampoo/conditioner out of your hair with this method - it's a common cause of dandruff and, occasionally, hair loss.