Sharon, all i can do is share what we are advised here in Australia - i know people do things differently everywhere so it is up to you...
having said that, we are advised to use boiled water and sterilize all bottles/teats until 12 months. i guess there was a reason i was still doing it and not just habit - obviously i remembered being told this...and confirmed it yesterday.
i guess there is always a SMALL risk that something can contaminate the water, corrosion in your pipes, etc and although they eat dust bunnies and solids they would be less able to cope with ingesting somethign from the water... KWIM?
i'm just going to keep doing it and if i get stuck without water at hand i will use filtered tap water and not stress that 1 in 20 times it happens...