Waer heater. Also there is a second set of electrical connections which are for lights under the counters, Aisle lighting etc. The positive wiring is under a cap, the negative is the bus bar shown. The water heater 110 V circuit was moved from under the aft dinette seat to under the galley. The water heater thermostat is easily accessed. One can turn the temperature of the water heater up, because there is a mixing valve, which limits the shower water temperature. This feature allows for hot water to be utilized for several showers (brief) from a small water heater.