Do you need to disinfect a few batches of water to make them safe to drink? You can do this easily by setting a few bottles of clear water out in the sun for the duration of the day (or over two days if it’s 1/2 cloudy). This method, called SODIS (i.e. “SO-lar DIS-infection”), uses the sun’s UVA rays to effectively kill bacteria and viruses. One requirement is that the water in the bottle be clear enough to read through. If you’re starting with dirty water, you should strain it through a clean cloth and let it settle first.
(Note that this method won’t actually filter the water — it will simply kill pathogens. But there are easy ways to filter water, using a quick sand filter or, if you have a more permanent stationary installation, a biosand water filter.)