So when water starts to run out, as is happening in northern China, southern Spain and the western United States, among other places, farming tends to offer the best potential for thrift.

• 所以一旦出现水资源要枯竭的趋势，正如中国北部、西班牙南部和美国西部等其他地区那样，最有可能减少水供应量的往往是务农活动。