H2O Megamaser Cosmology with the ngVLA As a complement to observations of the Cosmic Microwave Background, a measurement of the Hubble Constant at z < 0.5 provides a powerful test of LCDM cosmology and constrains the equation of state of dark energy. Observations of circumnuclear water vapor megamasers at 22 GHz in nearby active galaxies can be used to measure distances to the host galaxies, geometrically, and thereby provide a direct, one step measurement of the Hubble Constant, independent of standard candles. Observations of megamasers with present-day instrumentation are expected to reach a ~4% H0 measurement. A long-term goal of the observational cosmology community is to attain a one percent measurement of H0 in agreement across several independent methods to minimize the systematics. We will discuss the opportunity to reach a ~1% H0 measurement using the megamaser method by taking advantage of the sensitivity at 22 GHz afforded by the ngVLA.