Once a single-serve plastic water bottle is consumed it does not just disappear when it is tossed into a garbage can.

Source: Treehugger
Of the 80 million single-serve bottles of water consumed daily, 30 million end up in landfills. That stat is old data as of 2009. As of 2018, I can assure that it is much much more.
If those > than 30 million bottles do not make their final resting place in a landfill, they could either be incinerated or become a disturbance in natural ecosystems. I see them all the time!
In a perfect world, we wouldn’t be so reliant on bottled water, but we are.
We are wasting valuable space in landfills by filling it with bottles that are perfectly recyclable. While not purchasing bottled water is the best option, recycling the bottles is the second best option because it reduces demand for landfill space.
Unfortunately, it does not help reduce the demand for oil because bottlers are not using recycling content anyway (Royte, 2008). Ironically, it is cheaper for bottlers to use virgin PET than recycled PET.
Great…
In an effort to combat criticism of high environmental and energy costs, some companies have turned to a new approach. The new approach, called ‘lightweighting,’ reduces the cost of production, the energy required for shipping, and the mass of plastic in landfills (Gleick, 2010).
These are the new eco-friendly water bottles with the flimsier plastic and smaller shape.
Regrettably, lightweighting does not increase recycling rates or reduce the number of bottles in landfills (Gleick, 2010). It definitely does not decrease the amount of bottles American purchase; it only helps them feel less guilty about it.