Chloride compounds are used extensively in industrial operations and agriculture. For example, the potash in fertilizer is potassium chloride. Common table salt is sodium chloride and is a necessary part of human and animal diets.

Chloride levels in waterbodies are affected by several factors. Climate is a major influence. For example, chloride concentrations in waterbodies in humid regions tend to be low, whereas those in semi-arid and arid regions may be hundreds of times higher because of higher rates of evaporation. Seawater often has a reported chloride concentration exceeding 15,000 mg/L, but the chloride levels vary considerably worldwide. Over 75% of Florida lakes have chloride concentrations that are less than 22mg/L. Waterbodies in the Florida LAKEWATCH database have average chloride concentrations ranging from 1.7 to 2300 mg/L.

The activities of people and animals can also affect chloride concentrations. For example, because chloride is found in all animal and human wastes, septic systems and areas where animal wastes are deposited may be sources of chlorides in waterbodies. Home water-softening systems and fertilizers also are sources of chlorides. For these reasons, the presence of chlorides can sometimes be used as an indicator of pollution from these sources.

Health Concerns
Chloride concentrations in lakes are generally so low that they pose no known threat to human health. Water will have a strong salty taste if chloride concentrations exceed 250 mg/L. It should be noted that although the chlorides are not dangerous themselves, they signal the possibility of contamination from human or animal wastes that can contain bacteria and other harmful substances. For this reason, it is prudent to investigate where the chlorides are coming from when high concentrations are detected in an inland waterbody.

The Role of Chlorides in Waterbodies:
Salts are the primary sources of chloride in water. (The term "salt" includes compounds in addition to table salt (sodium chloride)). Traveling by many pathways, chloride has found its way into all the world's waters. Many coastal waters have high concentrations of chloride because they are close to marine (i.e., saltwater) systems. In coastal waters, seawater can seep into them from underground (called "saltwater intrusion"), or flow directly into them through tidal flow. Also, sea spray carries chloride into the air where it can then enter waterbodies as part of rainfall, even far from coastal areas.

The saltiness, or chloride concentration, of water can affect plants and wildlife. For example, some species die in water that is too salty, and others die in waters that is not salty enough.