Mould is a natural and harmless microorganism that loves damp, moist spaces. When you think about it, that's precisely what your water bottle is a damp, moist space with minimal airflow. Bacteria, fungi and even mould can thrive in a water bottle, thanks mainly to its moist environment. Therefore, simply rinsing the bottle out with water isn't sufficient, and care must be taken when cleaning bottles that have attached straws and narrow-mouth lids with lots of nooks and crannies. Mould can cause health problems if inhaled or ingested. It may cause allergic reactions like asthma and allergic rhinitis. People with respiratory problems should avoid inhaling mould spores regularly because they might aggravate their condition. 

In addition to mould growth, bacteria can also grow in a water bottle. That's because the inside of your water bottle is exposed to all kinds of bacteria from the outside world — including the surface of your skin — and its own contents (the water). When you drink out of a plastic bottle, it picks up all sorts of germs from you, too - maybe even ones you've carried on your skin. Fungi can form on any material exposed to moisture and oxygen (like your plastic water bottles), but they're most common on rubber stoppers or lids that aren't sealed properly. 

Why does mould grow in water bottles? 

The main culprit behind mould growth in a water bottle is the lack of air circulation within the container. For mould to grow on the exterior of a water bottle, there must be some sort of moisture present within the bottle. This can come from condensation from sweat or moisture from other sources such as food or drinks contained inside the bottle. For example: If you put your favourite drink into a fully sealed plastic water bottle without any ventilation holes, then that drink will likely be absorbed by the plastic over time until enough moisture has accumulated inside for mould to grow inside the plastic container. 

Plastic or glass water bottles are especially vulnerable to mould growth due to their porous nature. Plastic bottles can be cleaned by scrubbing with soap and warm water or using an abrasive cleaner like toothpaste or liquid dish soap. When washing glass bottles, ensure you avoid using anything abrasive on them as this can damage the surface of the glass and make it more susceptible to mould growth. Straws and lids should also be removed before washing your bottle as these tend to hold moisture inside them, which makes them more hospitable to bacteria growth than other parts of the bottle itself - so only rinse the straws/lids under running water. 

Basic steps to clean: 

1. Add a mixture of white vinegar and water to fill your bottle. Let the solution soak inside your bottle overnight. 
2. Use a clean cloth to wipe down the surface of your bottle where you have removed the mould growths (do not use any cleaning products). 
3. Once you have wiped off any remaining moulds from your bottle, wash it using warm water with detergent soap or another mild cleaning product that suits your needs (e.g., dishwashing liquid). This will eliminate any remaining traces of the mould spores inside your bottle that may have been left behind on its surface after washing out with warm water alone (this method will only remove visible traces of mould). 
4. The next step is to rinse the bottle with water and vinegar. Pour the solution into a bucket, and scrub the bottle with a soft brush. Let it sit for about an hour, and then rinse it again with more vinegar solution. Repeat this process until there is no more mould in your bottle. If you still notice some mould after this process, repeat the steps above until you are satisfied that no more mould is left. 

Copper bottle: 

Cleaning a copper bottle can be tricky if you don't know the steps because copper can react with certain elements (warm water). So, the first step in caring for your copper water bottle is to clean the inside with vinegar, salt and water. This will help remove any dirt or germs inside your bottle. You will need 2 tablespoons of vinegar, one tablespoon of salt, and 1 cup of water to clean your copper bottle. Add these ingredients to an empty copper bottle and close the lid tightly. Shake the mixture thoroughly until all of the ingredients have dissolved into it. Pour this mixture out and fill your copper bottle with fresh water to become clean again. 

Steel Water bottles: 

When you have time to spare, it's also a good idea to use a toothbrush to scrub out any hard-to-reach areas that might have become dirty or stained over time. You can also use toothpaste as an alternative cleaning agent if you're worried about your plastic getting damaged by abrasives in regular cleaners. If you have mould growing on your bottle, try soaking it overnight in vinegar or lemon juice (this is especially effective if there's rust on the surface). Afterwards, rinse any remaining residue with hot water and let the bottle air dry before using again — make sure not to leave it sitting in sunlight for too long, or it could cause more damage.  

Tip: When purchasing Cooper and steel water bottles, go for a trustworthy source like TheBetterHome's Copper and Stainless-steel water bottles. They are durable, eco-friendly, lightweight, leakproof, and easy-to-wash.