The water bottles are located on each side of the humidifier secured with a locking feature. To release the bottles just hold the bottle, push down on the button and slide away from the unit. You will be able to see at the removable caps where you refill. This is easiest to fill from a faucet. The water tanks hold 1 gallon of water each so it is not too heavy to transfer once the bottles are full. When you are ready to reinsert the bottles, re-position them into the base and slide the bottles into place. Push down on the top buttons to click it in place. If you see a red light, this means your water tanks are empty and it is time to refill.