Water bottles are not the easiest of items to clean inside because of their shape, and yet it is important to give your bottle a thorough clean at least once a week.
Bacteria can build up on the inside surface even when using plain water, and this is worsened if you use drinks containing sugar.
There are several popular cleaning methods, dish soap, vinegar, baking soda, or a combination of all three. But these are all somewhat of a hassle, and there is always the problem of leaving an unpleasant after taste in the bottle.
This is one I use and I believe is a far simpler method; use Efferdent tablets or another similar brand designed to clean dentures by soaking.
Once you get over your initial feelings of repulsion, think about it. These tablets are: A.) Designed to kill bacteria by soaking, no scrubbing required, B.) Made to remove stains and will not harm plastic, and C.) Safe to use and leave no unpleasant after taste.
What I do is fill my bottle right to the brim with hot water (From the faucet, not boiling.) Put two tablets in if the bottle hasn’t been cleaned for a while; one is okay if you are doing this on a regular basis.
Open the drinking nozzle and set it upside down on top of the bottle so the inside of the nozzle is soaking. Allow to soak at least 15 minutes; it is also safe and even better if you let it soak overnight.
After soaking, replace the top and squirt the solution out through the nozzle to further clean the inside. When the bottle is half empty, close the nozzle and shake vigorously. Empty the bottle, fill with clean tap water and repeat. When you are satisfied the bottle is thoroughly rinsed, it is ready for use.
A box of 120 tablets costing somewhere around $6 will last over a year if you are cleaning two water bottles a week.