These are not as obvious as they might seem. Regulatory agencies the world over recognize that the offensive taste of iron in water is harmless and that toxic levels of lead or a pesticide may have no taste or odor at all, and regulations are always separated into mandatory health-related requirements and other aesthetic requirements which are only recommended. However, there are cross-overs, and others that cause problems only for equipment rather than for people. The recommended pH range of 6.5-8.5 becomes mandatory if there is a problem with corrosion of lead, copper, and cadmium plumbing materials. Excess sulfate or TDS (Total Dissolved Solids) causes short-term diarrhea in visitors unaccustomed to a water supply, but this is considered only an aesthetic problem. Likewise, excessive silver causes a deathly graying of the skin and the whites of the eyes, and excessive fluoride ion causes ugly stains and even malformations of bones and teeth, but these are not considered to be health problems. Too much zinc can cause vomiting, but since there is no permanent damage, zinc is also only an aesthetic contaminant. As for process nuisances, there is nothing toxic about silica or hardness and alkalinity, and there are no regulations for them, but in excess they can lead to very damaging and costly scale buildup. Similarly, turbidity is very important at the time of disinfection (when it must be very low), but its importance to our industry lies in its ability to scratch valves, add to scale, and plug filters.