There are several methods in the following link choose the better one for you

https://wikiwater.fr/e17-simple-water-treatment-methods

Can use anyone that suits you.

1) Keep the water for some 10-12 hours in a copper container which will eliminate all bacteria.

2) Neem (Azadirachta indica) leaves extract works as a good antibacterial agent, & you will have to standardize the dose to be applied.

3) Alternatively Neem oil seed cake also equally gives similar results.

UV light sterilization can work sir.

thank you Kiprotich Kiptum , actually UV has been applied. also it causes a great reduction in bacterial number, but it is not able to eliminate them all. even when it co-applied with UV.

Chandravadan Trivedi thanks

Have you tried the UV? Ultraviolet Sterilisation Systems can kill 99.99 of germs and bacteria in water.

Please do read a bit about the UV here:

https://silverlineuk.co.uk/product-category/uv-water-filters-ultraviolet-sterilisation-systems/?gclid=Cj0KCQjwk4yGBhDQARIsACGfAespRKOPYYlmVORECyfRekESG_UP09psSgsK0UOaVV2CCvZykTbX34EaAo_BEALw_wcB

the pore size of RO membrane is 0.0005 microns

if you are seeing 0.2 um you may have membrane integrity issues

Mohammad Hossein Abbaspour interesting question and there are many ways of quick and best ways to treat water and avoid polluted water but again it depends on the economics as well as the size of the plant or amount of water to be treated on a daily basis so one can come to a conclusion with the amount of water to be treated and for what purpose is also to make an economical feasibility option to select the best possible available technology.

By nanotechnology.

On top of Srinivas Kasulla comment, please, be aware that the treatment method choice always depends on application, resources available, the requirements to treated water quality and local regulation (related to raw water consumption and wastes quality and quantity). There is no the best solution could fit all the potential cases (even if you are looking for the way how to remove bacteria from water only).

Do you have an idea for the nature of the bacteria you want to eliminate? You don't say it!