pH is a measurement of how acid something is. The pH scale - it runs from 1 which is termed acid to 14 which is alkaline. Soap has an alkaline pH, vinegar has an acid pH. Water should have a pH of seven which is neutral. Always use a carbon water filter for your tap water. Now, all chemical systems function most efficiently at a specific pH. For example, a swimming pool should be 7.2-7.6; as long as the water pH is in that range, the pool is healthy. If the water gets a little too acid pipes began to corrode, grout is eaten away, so what does the pool owner do if the pool water is too acid? He will add alkaline. Very simple. If the water gets too alkaline, algae grows in the water. So then the pool owner will add some acid. Our Bodies pH is very important -- Our body likes a pH of 7-8. As long as we are in that range, our body is healthy. Our blood pH is 7.4. If the blood pH drops to 7.2 we will die. All the red blood cells stick together, they don't carry any oxygen and we die. It's called acidosis. Now that isn't much tolerance is it? 2/10 of one percent.