Commodity products like bottled water have fierce competition. Besides taste, quality and nutrients, packaging plays an important role in the brand positioning of such products.
The 1 liter plastic bottle for water has been there for many years, along with bigger and smaller versions.
However, these bottle designs miss a few things:
For the 1 liter version, either you have to drink the full bottle during a short time or the water becomes stale/warm after opening it, so you do not feel like drinking it later, specially the next day onwards.
You can buy the smaller versions of this bottle and carry them in your car easily. However, if you are traveling by public transportation, you have to manage carrying many of these, which feels cumbersome and is not sleak.
If you have a 1 or a 2 liter bottle while you are traveling with friends/family, it is difficult to share the water unless you have glasses.
One more issue is that you are forced to gulp the water from the bottle, instead of sipping it , which you could do if the bottle had a built in straw.
An alternate design for this bottle could be a small (half pint sized or smaller) bottle, with a modified base which allows another similar sized bottle to be connected to it. This could be achieved by putting grooves/threading on top of the plastic cap to screw/connect the bottle to the bottom of this modified bottle base. Connecting 3 to 4 of these together would make it easy and sleak to carry. It would keep each unit separate from the remaining ones, water could be shared with friends easily, and would keep the water fresh(since all bottles do not have to be opened).
Another degree of improvement can be achieved by changing the design so that the water can be kept cool for a long time. Will leave that for another day..