Although drinking fluids is absolutely crucial to good health, and water is often the healthiest certainly the lowest-calorie option, using tap water rather than bottled water is important for both our health and for the health of our environment. If taste is an issue, filtered tap water is a solution.
Commercial water bottles including the small ones we carry around and then throw away, the larger gallon-sized bottles we may buy for our refrigerators, and the larger 5-gallon polycarbonate containers found in offices and other public spaces often are made from plastics that leach chemicals like Bisphenol A, which is known to mimic hormones, and which has been linked to an increased risk for breast cancer and other diseases. Leaching of chemicals from plastic bottles is particularly common when the plastic bottles are warm, as can happen when bottles sit in the sun. If you are using a plastic bottle and the water or other fluid inside it smells "plasticky", dont drink it! Your nose is telling you good information about the presence of contaminants in the water.
Of course, there are loads of other reasons for not drinking bottled water whenever possible. Tap water is often as safe or safer than bottled water, as public water sources are closely monitored and the results of quality testing on these waters are available to the public. Similar testing and disclosure are not required for bottled water.
And of course, the plastic required for commercial bought bottled water is a huge drain on natural petroleum resources, and adds enormously to our communities' waste burden.
To take water on the go, invest in a cheap, high-quality stainless steel water bottle, or another reusable BPA-free water bottle.