Read the excerpt from "Water Flowing from Toilet to Tap May Be Hard to Swallow."As California scrambles for ways to cope with its crippling drought and the mandatory water restrictions imposed last month by Gov. Jerry Brown, an array of ideas that were long dismissed as too controversial, expensive or unpleasant are getting a second look. One is to conserve more water; another is to turn nearby and abundant sources of water, like the Pacific Ocean, into drinking water through desalination.Yet another is to recycle the water Californians have already used. And therein lies a marketing challenge that can be even greater than the technological one.