You might find this article of interest, Matheous.
http://www.abc.net.au/health/talkinghealth/factbuster/stories/2010/10/27/3048695.htm
I assume your concern relates to phthalates being suspected of belonging to a class of chemicals that can potentially disrupt the endocrine system. Disruption of the hormones and the regulatory pathways could indeed be potentially quite serious, but the problem is that the science associating the link between phthalates and endocrine disrupters is scant and not particularly well demonstrated.
Then you have issues about just when in our life cycle such an endocrine disrupter might be harmful, and most would concur that the greatest risk would be during the development phase - ie foetus/developing infant.
So - poorly articulated and demonstrated risk.
Next, do water bottles contain sufficient to cause problems, and does this leaching happen during normal use and storage? And again there are problems with making this link, because PET is not the type of phthalate thought to be a problem for a start. Secondly, the idea that leaching occurs at all is still not proven very well, and thirdly, even if the leaching does occur, it occurs under exceptional circumstances - intense heat or re-use over a long period of time.
Personally, I think there are far bigger health risks to worry about, and if you are going to choose between tap water or plastic bottled water, you should recognise that bottled water does far more harm to your wallet than it likely is to your health! :)