The water quality of creeks can vary from pristine to hopelessly polluted with heavy metals from mining slagheap runoff or pesticides from farmland runoff. There's nothing you need to do in the first case and nothing you can do about the second one. While industrial pollutants are not frequent in the backcountry, you should determine if you might encounter them in the area where you would like to hike.

Generally speaking you don't need to worry about viruses in surface water in backcountry areas. The commonest hazards are bacteria or cysts such as cryptosporidia. Any of the filters commonly sold to backpackers and hikers will do a good job of removing these, if you use them with care.

I've recently switched over to using the Sawyer Mini. It is small, light, fairly inexpensive and easy to use. In the past I've used the Katadyn Hiker filter with good results. These are the only two I have direct experience with. Both worked fine.