evidence: Acidic water is synergistic, which means that a combination of a low pH and an increased concentration of certain substances is far more harmful than the sum of the parts. For example, aluminium, lead and mercury are potentially dangerous substances, but when the pH of the water source is already low, these substances can have extremely detrimental consequences for aquatic life. Acidic water can also cause problems for human consumption. While slightly acidic water is not dangerous, on its own, it can be quite dangerous when combined with other compounds. Water with a pH that is less than 6.5 can leach metal ions, including iron, manganese, copper, lead and zinc from plumbing fixtures and pipes. This, in return, can be quite dangerous. On the other end of the pH scale, water that has a pH greater than 8.0 can be difficult to disinfect. The World Health Organization recommends that the pH of the water be less than 8.0, because basic water does not allow for effective chlorination. [...] Like TDS, pH is given an aesthetic objective in Canada. The Canadian Guidelines for Drinking Water Quality suggest that the pH of drinking water should be between 7.0 and 10.5. The Saskatchewan Drinking Water Standards and Objectives recommend that the pH of drinking water be between 6.5 and 9.0.