While not a particularly reliable method, solar water disinfection (SODIS) can help supplement any other methods you’re using to purify water.
All you need is the sun, some clear plastic bottles (not glass), and water (of course). Make sure the bottle is clean, especially on the inside, and that you can seal it.
Fill as many of the bottles as you have and can spare, mark them as SODIS containers to differentiate from your storage bottles, and leave them in the sun for a full day (minimum). The sun’s UV rays will kill or damage most biological contaminants.
While not guaranteed or thorough, it will also reduce bacteria and viruses in the water.
There are some shortcomings to this method, which you need to bear in mind if it’s your primary means of purifying water.
First, as mentioned, it won’t kill all biological contaminants, especially not all bacteria and viruses. Second, SODIS has no effect whatsoever on chemical contaminants. Third, you need at least one full day of sunlight or two overcast days for it to work at all.
Finally, there’s the obvious limit to how much water you can treat at a time. This will be dictated by the number of clean, usable plastic bottles you have. Over time, these are likely to warp and/or start leaking their own chemicals into the water.
But in a pinch, it’ll do – especially if you follow it up with boiling (leaving your pot free for cooking and heating washing water in the meantime). And one major benefit it has over stove/fire top and solar distillation is you don’t need to keep a constant eye on it!