If it is for an emergency ...

If it is for an emergency situation, like post-disaster, then the first thing that should be taken into consideration is that it is economically viable without compromising it's purification abillity. As your target population is very small, you should not try to invest a huge amount when affordable alternatives are present. Also, identify the major contaminants present or possible in the near future in the drinking water of that area and then proceed with the relevant purification technique.