The beauty of the reusable water bottle is that it's just that — reusable. You can repeatedly head to the water cooler or faucet to fill it up, but when your bottle continually stays wet, it doesn't have the chance to get a proper cleaning. Since bacteria love a moist, dark environment, it's good to get in the habit of cleaning your bottle every night — or at least every few days. Here are some ways you can get rid of the germs and grime.
Throw it in the dishwasher: Some bottles are dishwasher safe, so check the bottom of your bottle or the brand's website to make sure. Kleen Kanteen Classic stainless-steel bottles and glass bottles like those from Lifefactory and bkr  are dishwasher safe, as well as some products from Nalgene  and Camelbak.
Wash it with warm soapy water: Pour out any leftover liquid, add a few drops of dishwashing soap and some warm water, screw on the top, and shake for a minute or so. It's smart to invest in a bottle brush like this  so you can scrub deep inside your bottle, especially if it has a narrow mouth. Thoroughly clean the cap and straw as well and allow to air-dry overnight.
Use vinegar: This all-natural cleaner is great for killing certain germs and bacteria, but it isn't effective at killing everything such as the flu virus . If you're OK with that, use this method: after washing with soapy water, rinse well, and fill your bottle one fifth of the way with white vinegar . Fill the rest with water, let it stand overnight, and in the morning thoroughly rinse it out.
Use a weak bleach solution: If you're really worried about germs, nothing stands a chance against a little bleach. It's perfectly safe to drink from a bottle that's been cleaned with a weak bleach solution  — it can even be used to sanitize baby toys and bottles . Make a bleach solution using one tablespoon of bleach per one quart of water. Fill your bottle, screw on the top, and allow to sit for two minutes. Pour out the solution and allow it to dry out completely.
Use water bottle cleansing tablets: Many companies make this type of product, including Camelbak  ($12 for eight), or you can also get away with using effervescent denture cleaning tablets  such as Efferdent. Just fill your bottle with water, drop the tablet in, and allow to dissolve and sit for 15 to 30 minutes (depending on the product's directions). Then rinse and enjoy your clean bottle.