[单选] Standing in the shower waiting for the water to heat up could be a thing of the past， along with all the wasted water． Three and a half years ago， Lindy Honeychurch， a thirty-year-old Australian full-time mum living on a farm outside Launceston， didn"t consider herself a very good water saver． Neither did her partner who often complained about it with good reasons． Their farm had to rely on tank water and solar power， which meant water had to be trucked in if the tank water ran out in summer． "I looked at where I could save because I could lead an easier life without the complaint，" she said． Modeling her idea on a car thermostat （恒温器）， Lindy used her kids" magnetic （磁的） drawing board to design a device that diverts the cold water back down the hot water pipe． "The first aim when I started designing was to keep it really small and simple without having to use power． I wanted to keep it as something that everyone could use，" said Lindy．What does the second paragraph mainly about？