Water filters aren't the only way to purify your drinking water. Boiling is one traditional method. But while boiling is highly effective, it does have its drawbacks. For one, it's time consuming to purify a significant amount of water this way. And, while warm water may be a treat when you're on a winter hike, it's certainly not when the weather is toasty. Even after allowing the water to cool, you'll be drinking tepid water.
Boiling also has a negative effect of the taste of the water. Some people describe the taste as "flat." You can reduce this somewhat by pouring the boiled water back and forth between two clean containers as it cools. This process aerates the water, improving the taste. Probably the biggest drawback of boiling is that you'll use a lot of fuel to boil enough water to keep you hydrated.
Chemical tablets are another option for purifying water. These tablets typically contain iodine. They do a good job of killing bacteria in the water and making it safe to drink, but they have a negative effect on the water's taste. Water treated with iodine is bitter and has a lingering aftertaste.
Also, while they're inexpensive, once the bottle of chemical tablets is open, it has a limited lifespan. Another drawback of chemical water treatment is that it doesn't always work against some types of protozoa. Finally, if the weather is particularly cold or the water is filled with sediment, the chemical tablets will take longer to work.
The biggest drawback of chemical treatment is the adverse health effects it can have on some people. For people with thyroid disease, immunodeficiency and some other health concerns, chemical tablets containing iodine can be a serious threat. Also, if you're pregnant, it's important to speak with a doctor before using iodine for water purification.