1. Water Filters.
2. Chemical treatments.
3. Boiling the water.
4. No treatment at all.
"safe" natural springs versus contaminated water sources.. I don't really recommend this as a way to obtain good drinking water, but it can't hurt to learn how to find the natural sources that are most likely pure. A filter can clog or your water tablets get lost.
Rainwater collected in clean containers or in plants is usually safe for drinking. This is just something to remember for emergencies, though. Always purify water from lakes, ponds, swamps, springs, or streams. Even deep in the wilderness, most water sources now have Giardia or other unhealthy bacteria and viruses.
Water purification by boiling works fine. Just boil for a minute or two and you are usually okay. The problem is that it is just too much trouble for backpacking. Do you want to stop several times daily to set up your stove and boil enough water to fill your water bottles? Do you want to always need a good fire to do the same, or to carry the extra fuel for that stove? For regular use, there are just two convenient ways to purify water when backpacking. They are water filters and chemical water treatments.