At the height of the 1960s ‘flower power’ hippy era, visitors to San Francisco were encouraged, in a number one hit song, to “wear some flowers in your hair.” A half-century later, visitors would be better advised to bring drinking water, after the publication of test results indicating that all the city’s supply is likely unfit for consumption. It’s not the only place concerned about the state of drinking water, and a recent survey analysis shows more than half the world’s people expect their drinking water will make them ill. “Samples from bottled water, tap water and household-treated tap w…