If wanting to heat the water only in order to reduce pathogen exposure, there may be alternatives. I know some people were dealing in an area where the water bodies and water supply were likely to be highly contaminated by even decomposing animal and human corpses, and one product that kept coming up was "Lifestraw" filtration products. But a lot of the more portable filtration products that are around are better used when the water to be filtered is not yet heated.