Today I was able to do a quick test of the first installed sprays of the External Water Spray System (EWSS). Very impressive.
I've also integrated the rainwater system and garden sprays into the system. All water supplies (town, fire tank, and rainwater) now all feed into the one manifold so that the fire system can use the garden sprinklers. The fire hose lines still come straight off the pump for absolute reliability.
I've also updated the system documentation including the hydraulics diagram on my wiki here.