Note the greenish black ring at the bottom of this plastic bottle. It has outlived multiple dishwasher cycles and vigorous bottle brushings.
But according to the bike discussion groups I hadn't gone nearly far enough:
I take a cap full or so of bleach and dilute it in about 8 ozs of water and throw it into the water bottle and fill it up with water. The mix is about right if it has a nice distinct chlorine smell still without being overpowering. Then fill with normal tap water, let sit for a few hours and repeat a few times. The bleach will kill virtually all the microbial stuff. It is a reasonably good disinfectant. Put the bottle in your freezer overnight to kill any residual mold.
I use well water, so no chlorine in the water here either. Whatever you use to clean, make sure you scrub too. Otherwise, the killed stuff sticks to the bottle and provides a medium for new growth. As for what to use, bleach water is still the first choice, but not full strength! Fill with water, add a few tsp of bleach and let it sit overnight, then wash with dish water afterward. Other sanitizers you could use would be rubbing alcohol or Windex-type surface cleaner. (Make sure you wash thoroughly afterward.) Or you can use denture cleaning tablets or mouthwash if you want something with a less toxic aftertaste.
Then there is the sand and gravel approach:
1 Fill the bottle with sand, gravel and water.
2 Shake for ten minutes
3 Empty, clean with brush and soap.
4 Repeat steps 1--3 several times, adding different grades of fine gravel.
I desperately needed to devote less of my life to cleaning plastic water bottles. So I kept searching for an alternative that would actually work.
A few weeks ago I was delighted to discover the CLEAN BOTTLE which incorporates a revolutionary concept: a "leak-proof" removable bottom cap. It makes cleaning a water bottle easy.
After several rides and subsequent bottle cleaning cycles I haven't seen a speck of mold or discoloration inside the Clean Bottle. Post ride cleaing takes less than a minute with soap, warm water and an ordinary bottle brush. No sand, no bleach (!), no gravel, no denture solutions or mouthwash, no overnight freezer treatments.
On rides my water stays in the bottle and tastes fine. What more can you ask from a bottle? The electric blue cap will soon be augmented with a line of colors to match just about any bike frame. Clean Bottle has come up with a simple solution for a needlessly complex problem.
For a short history of the bicycle water bottle——and a further endorsement of the Clean Bottle,——see this Road Bike Review article.