Fresh potable water is one of most important things you will need in any survival situation. Although it typically requires lab testing to be sure water is safe to drink, here are some water disinfection steps that can be taken to reduce the risk of consuming water you have obtained from your environment.
Start with the cleanest and most likely to be safe water you can find. Use water filtration techniques to remove as many particles, chemicals, and bacteria as possible. Then kill the remaining bacteria with one of the following methods to disinfect water:
Boil Water Disinfection
Boiling is considered one of the best ways to disinfect water for consumption. It is possible to use the intense heat from a fire to boil water and dis-infect it from many pathogens and bacteria. The water will need to be placed in a metal container or pot and placed on the hot coals of the fire. The water should be brought to a roaring boil and then kept there for at least three minutes.
Solar Water Disinfection
It is possible to take water that is relatively clear and place it in PET plastic bottles (such as common 2 liter bottles), and then utilize the natural UV rays from the Sun to kill off bacteria. The water must be as clear as possible, and it is important to know that some types of glass and even types of plastic will block UV rays, reducing the effectiveness of this technique.
Colorless, transparent PET water or soda bottles (2 liter or smaller) with little to no surface scratches are best. Leaving an air space and shaking the bottle after filling may increase the effectiveness as high oxygen content in the water helps.
The bottles should be placed in the Sun for a minimum of 6 hours on a sunny day, and 2 days if it is cloudy. The water should ideally be kept in the bottles until use to reduce the chance of re-infection.
I like to keep a good supply of suitable bottles in my reserve fresh water supply filled with known clean water before a disaster strikes. As the bottles are used, they can be refilled and then used for solar disinfection to help sanitize the replacement water. I will routinely use the bottles in a rotation for watering house plants, filling pet bowls etc. so that that the water is kept fresh.