To naturally purify water, make a DIY filter using layers of gravel, sand, and charcoal in a container. The gravel removes big particles, while sand and charcoal capture smaller impurities. Charcoal helps by adsorbing contaminants. Let the filtered water sit in sunlight for disinfection or boil it to kill bacteria. Combining these methods creates a simple and cost-effective way to purify water, useful in outdoor or emergency scenarios.

Rinsing a filter in tap water can introduce impurities and contaminants from the tap water back into the filter. The purpose of the filter is to remove these impurities, so using tap water for rinsing undermines its effectiveness. It is recommended to use clean or purified water for rinsing to maintain the integrity of the filter and ensure that it continues to effectively remove contaminants during use.

The most effective way to filter tap water for drinking is to use a reliable water filtration system that employs activated carbon filters or reverse osmosis. These systems can efficiently remove a wide range of contaminants, including chlorine, sediment, heavy metals, and other impurities. Additionally, regularly replacing the filters in these systems is crucial to maintain their effectiveness. If a filtration system is not available, allowing tap water to sit and settle for a while and then using a fine mesh or cloth filter can help remove larger particles. Boiling tap water is another simple method to kill bacteria and parasites. 

No single water filter can remove all contaminants, as different filters are designed to target specific types of impurities. However, a combination of filtration technologies can provide comprehensive purification. Activated carbon filters are effective against organic compounds, chlorine, and some chemicals, while reverse osmosis systems can remove a wide range of contaminants, including heavy metals and microbes. UV purifiers are efficient in eliminating bacteria and viruses. Combining these methods in a multi-stage filtration system or using a comprehensive filter that incorporates multiple technologies enhances the ability to remove various contaminants, resulting in cleaner and safer drinking water. 

Boiling tap water is not effective in removing PFAS (per- and polyfluoroalkyl substances). PFAS are persistent chemicals that can withstand the boiling process. To reduce PFAS in drinking water, specialized water treatment methods such as activated carbon filtration or reverse osmosis are more effective. These methods can help capture and eliminate PFAS contaminants, providing a more thorough and reliable means of water purification compared to boiling alone.