The waters of Lake Arrowhead flow to Deep Creek and of course past the hotsprings. The dispute over the water use in Lake Arrowhead will affect Deep Creek.
It is interesting the the State Water Resources Control Board came up with the decision that the water was for "recreation only, and not for other uses, specifically not as a source of drinking water."
http://www.sbsun.com/news/ci_3188139
However, water is a right developed by use and the early pioneers who settled around Lake Arrowhead would definitively used the water for domestic uses, lumber uses, and irrigation uses.
I have been involved in reviewing the recorded documents concerning the water rights of Lake Arrowhead. The documents do speak about domestic water use.
However, Lake Arrowhead is within the San Bernardino National Forest and its primary purpose is recreational "for the enjoyment of the American people".
If the final decision is that the water is for recreational purposes, then you should see an increase in the water flow in Deep Creek.
But there is development looming for the area around Lake Arrowhead and water is a requirement for development. Large water storage tanks have been recently installed in the area. Water has become extremely valuable and sought after. The residents around Lake Arrowhead were recently assessed with $54 million over their domestic water needs.