Plastic bottles are certainly ubiquitous--they bring us everything from household cleaners to soft drinks to things so readily available as water. These bottles, while convenient, do have disadvantages when used on as wide a scale. While most of these disadvantages are environmental in nature, the consequences could have widespread economic consequences in the long-term.
The main disadvantage of plastic bottles is the shear amount of time they take to decompose--the average plastic bottle takes 500 years. Plastic's decomposition can be affected by various factors, such as the type of plastic, the climate and acids in the landfill; plastic still lasts a long time, filling landfills for an indefinite period.
Difficult to Recycle
Glass bottles can be melted and easily reused, as can tin cans. Recycling plastic is not so simple. Much of the plastic placed in recycling boxes is not recycled at all, as most plastic cannot be recycled. Those bottles that are recycled are not used to make new bottles. Instead, recycled plastic bottles are used to make non-recyclable products, such as T-shirts, plastic lumber or parking lot bumpers. This means more raw materials need to be used to create new plastic bottles than is the case with easily recycled material, such as glass or tin.
Hard to Reuse
The standard disposable plastic bottle is meant for one use, not many. Recycled plastic bottles are not refilled in-mass the way glass beer bottles are, and flimsy plastic bottles do not lend themselves well to at-home re-usage. Water bottles, for example, are often reused in the home but become less and less sturdy over time and are ultimately thrown away.
Plastic is manufactured using oil by-products and natural gas, materials that could be used in numerous other applications or conserved were plastic usage lower. Natural gas, for example, can be used to heat houses and cook food. Using plastic in the volume we currently do reduces the availability of these resources, which are gone forever when used up.
Things You Can Do
The two best things you can do is to use less (or no) plastic and to reuse plastic when possible. Many products that come in plastic bottles are also available in glass bottle or tin cans; use these whenever possible. Instead of buying bottled water buy a refillable water bottle and fill it with tap water. Generally, try to waste less by using less and reusing when possible.