I have a 1.5 liter plastic water bottle (the disposable kind) that I keep on a shelf by my bed. I fill it every night before bed, and generally nearly finish it by the morning and refill it when I wake up. I recently noticed that I've been using the same bottle for months... is there any issue with this? Any mold concerns, etc? Or can I keep using it indefinitely?
The general prescription for water bottles is to recycle them, not reuse them. According to a University of Virginia paper:
Reuse of polycarbonate plastic bottles is generally not recommended by commercial bottled water manufacturers, as it may pose a health risk from two perspectives. First, everyday wear and tear from repeated washings and reuse can lead to physical breakdown of the plastic, such as visible thinning or cracks. Bacteria can harbor in the cracks, posing a health risk. Secondly, reuse of plastic water bottles can lead to bacterial contamination unless washed regularly. If a consumer wishes to reuse a plastic water bottle, it should be washed after each use in mild detergent only and rinsed well (9). The plastic should not be subjected to extreme, hot temperatures or harsh detergents, and should be carefully inspected for physical breakdown prior to reuse.
Additionally, the narrow opening can make it difficult to clean and dry properly.
Another issue not addressed thus far is contamination by the breakdown of the plastic bottle itself. Here's a quote from the Environmental Working Group:
Hard plastic bottles (#7 plastic) can leach a harmful plastics chemical called bisphenol-A (BPA) into water. Carry stainless steel or other BPA-free bottles. Don’t reuse bottled water bottles. The plastic can harbor bacteria and break down to release plastics chemicals.
If your water is hard, you'll get mineral buildup. I've found algae, green/orange, growing on those mineral deposits. Likely bacteria and fungus grow there too. I clean the container out with vinegar then detergent every month or so. That seems to keep the growies down to unnoticeable levels.
From a safety standpoint, you should probably autoclave your bottle every morning.
There was a case in Italy where the death of the girl was blamed on the water bottle she always used. It was then proclaimed by experts on TV to NOT be safe, so I'm discarding them now after I while. I can't find the story on Internet now, but I saw it on TV there. You can do some more research if you want.
I also noticed my bottle I use for running acquired a bad taste and smell after a year, although being washed.