drink the water from the bottle and don't spit any water back into the bottle

no just sparkling

you can heat the water up (to kill the germs and bacteria) while its inside the bottle and put the handkerchief on top (it will act as a filter) and clean water

To get it thoroughly clean, you need to empty what was in it first. Then you need to take warm water and fill the bottle. Let it soak for a few minutes to an hour depending on how clean you want it. After it just pore the water out and voilà!

To clean a water bottle you have to put fine sand into the bottle and then pour water and put one of your fingers to plug the bottle and shake for a little while and pour the sand and water out then rinse. Make sure the sand is gone. If you don't wash the bottle at all it will get moldy. Another way is to get a very small brush, stick it inside the bottle and scrub.