Best to buy yourself a good water filter, I have one of these
http://www.freshwaterfilter.com/prod...)_Home-GS2-SCD
I put tap water through it but it is ok to use with rain water as well.
This is the sort of thing you can use to drink water from puddles or rivers
http://www.backpackinglight.co.uk/product357.asp
Don't waste your money on bottles of water, you will save money in the long run if you buy a filter and bottle your own, remember to use glass bottles and not plastic as the plastic can leach rubbish into the water.