How is the water heater in Quantianxia filled with water?

Isn't this already connected? Blue is cold water, which is the water supply pipe. Open the eight-character valve (not on the water heater, but the pressure reducing valve), then open the eight-character valve of hot water, and then turn on the faucet that uses hot water until the water comes out, so that the water in the water heater is full. When in use, hot water is pushed out by cold water, so there is no need to worry about the water heater burning out.