evidence: Imprecise: The reason why acidity in bottled drinking water would be bad for health is not explained in the video. [...] Some people may have concerns about whether the pH of food and drink could significantly alter blood pH and thus affect our health, with some also believing that it is better to maintain alkalinity in their diet and that acidity is unhealthy. This belief is encapsulated in this video – shared on Facebook more than 1 million times – showing someone testing the pH of various brands of drinking water using a liquid pH indicator (which changes color depending on the pH), and declaring water with an slightly acidic pH –between 5 and 7– to be "bad". In truth, many liquids that we take in, such as fruit juices (e.g. orange, lemon, tomato), have an acidic pH – some are even much more acidic than those reported in the video – and yet fruit juices are generally considered to be healthy. Because pH levels are measured on a logarithmic scale, a difference of 1 unit corresponds to a factor of 10 (or one order of magnitude) in hydrogen ion concentration, so orange juice with its pH of 3 is ten thousand times more acidic than water with a neutral pH, and a hundred times more than water with a pH of 5. In other words, you would need to drink 15L (~4 gallons) of the more acidic bottled water shown in this video (pH=5) at a given time to achieve the same acidity as a glass of 0.15L of orange juice (pH=3).