Think you’re cleaning your water bottle enough? Wrong.

Q: How do I properly clean my reusable water bottle? And how often should I be doing this?

A: That’s a good question, if for no reason other than it shows you know it’s an issue. Many people believe that if they put only safe-to-drink tap water into a water bottle, there’s no need to clean it. After all, what goes in is clean, so what’s the worry?

If you in fact put only water in your bottle, rinse it each evening and let it air-dry overnight, or get two bottles and cycle between them, that may be fine. It’s when the interior stays wet that bacteria and mold are most likely to multiply, so the interior really needs to dry.

Here are some best practices for cleaning your bottle:

• Wash the lid with soap and water regularly - each day, ideally, because that’s where your lips transfer germs. Follow that routine and you might not need to deep clean, although that never hurts.

• In some cases, though, you should clean with soap and water after each use. That includes if you leave water sitting in the bottle or you fill it with something other than plain water.

• Molds and algae can also grow and form a slimy surface inside. It’s even worse if you put in sugary drinks, which leave residue that helps bacteria and molds thrive. Even residue from black coffee creates an environment that can increase microbe growth.

• Use a disinfectant and soak it for a bit if you sense a foul odor, see or smell mold, or find caked-on bits in the bottle.

• Letting grime accumulate on the outside of a water bottle also has consequences. It increases the chance that you will get some of that grime into the water inside the bottle while you are opening or closing the lid.

REI, an outdoor gear supplier that sells an array of reusable water bottles and hydration systems, agrees that rinsing and air-drying is fine in most cases, but offers some recommendations for when more is needed:

• Put a teaspoon of baking soda and a teaspoon of chlorine bleach in the bottle, then fill it with water and let it sit overnight. (Mixing bleach with some cleaning agents can release toxic fumes, but it’s okay to mix bleach with baking soda. Both are strong alkalis, and baking soda boosts the effectiveness of bleach and reduces its residual odor.) The next day, rinse out the bottle or put it in the dishwasher if it’s a model that can be cleaned that way. Let the bottle dry completely before you reuse it.

• If you don’t want to use bleach, try baking soda and hot soapy water. Or use white vinegar or lemon juice and hot soapy water.

• If your water bottle is stainless steel, baking soda without bleach is best because bleach can make the metal look dark and dull.

• If your water bottle has residue from smoothies or juices, you might need to put a little muscle into the cleaning. Many water bottles are too tall or have necks that are too narrow to effectively clean with a sponge or washcloth. But wander down the baby aisle at a store that caters to parents and you will find bottle brushes with sponge tips that reach into the bottom of a water bottle and allow you to scrub there without scratching the surface. You’ll also find narrower brushes that work great for cleaning straws or sip tips on water bottles, as well as short wands with fuzzy tips that reach into crevices in the multipart lids that some water bottles have.

• REI also suggests using anti-bacterial mouth wash to get rid of foul odors.

Cleaning reservoirs of hydration systems is more complicated because the interior surfaces are harder to reach. CamelBak sells a cleaning set ($12 at camelbak.com) with a brush that has a handle shaped to fit into the recesses of a reservoir, and a narrow brush on a cable for cleaning the drinking tube. Platypus makes a similar set ($15.95 at platy.com).

Follow these steps:

• To clean the reservoir, fill it most of the way with hot water. Add your choice of cleaner: For each liter the reservoir holds, use ¼ cup baking soda, ¼ cup lemon juice, or 2 to 5 drops of chlorine bleach, stirred into ¾ cup water. Or you can use tablets made for cleaning dentures or tablets made specifically for cleaning reservoirs.

• Close the reservoir and shake it to mix the cleaner and water. Open the valve on the drinking tube briefly, just until the tube fills with the cleaning solution.

• Let the cleaning water sit for about 20 minutes unless you are using tablets, in which case follow instructions on the label.

• Drain the water and disassemble the reservoir, tube and valve. Wash and scrub everything with warm, soapy water. Rinse thoroughly and let everything air dry.

• Do not put any of the parts in a dishwasher.