Bottled water. Fantastic if you are out and thirsty. The problem is what happens to the bottle afterwards? Some reuse the bottle. Others recycle it or simply just throw it away. For some people, bottled water has become the only water they will drink even if they live in a place with perfectly adequate water even though bottled water is less regulated than tap water. This leads to enormous amounts of waste (about 50,000,000 [50 million] bottles in america last year). These bottles require a huge amount of energy and oil to produce and transport.
Instead of buying bottled water, I pledge to use a long lasting reusable drinking container and tap water. In places where tap water is unsafe, I will treat it (either using a Steripen or purifying tablets). If offered bottled water, I will refuse it.