A portable hot water heater for larger-scale applications including emergency use, situations involving hazardous materials, and the like. The hot water heater advantageously efficiently and rapidly heats large quantities of water for providing a stream of hot water for immediate use. The hot water heater includes a pump that can draw water from any suitable water source, a power source, a heating assembly that quickly and efficiently heats the water as it flows through the heating assembly. The heating assembly is attached to a shower head or other fixture.