Abstract: A portable modular water heater system having a heat exchanger and a fluid heating channel for heating water from a reservoir and for optionally producing purified potable water. Optionally, a thermoelectric module is included in the system for producing an electric current usable to rechargeable batteries, drive pumps, or other devices. When the heat exchanger module is exposed to a heat source, heat absorbed by the heat exchanger is transferred to the fluid heating channel, heating the water. The heated water is forced into an upper portion of the reservoir. A condenser module is optionally coupled to the reservoir to condense steam in the upper portion. The thermoelectric module produces an electrical current when exposed to a temperature differential between the reservoir's cool water and the heat exchanger. A portable microclimate heating system, such as a jacket with tubing, can be heated with the heater system.