Glossary of Water Treatment Terms & Definitions - L

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Langelier Index

A calculated number that gives and indication of the tendency of water to form a protective film of calcium carbonate scale, to dissolve it or be in equilibrium with it. It does not take into account the quantities of film formed, the effect of velocities, oxygen, carbon dioxide, ammonia, silicon or natural inhibitors in the water. Therefore, it is sometimes erroneously assumed that any water that tends to dissolve calcium carbonate is automatically corrosive.

Leach Field

Area where septic tank effluent is distributed by underground piping for natural leaching and percolation through the soil.

Leakage

The phenomenon in which some of the influent ions are not adsorbed and appear in the effluent. It is usually caused by an under-regenerated exchange resin bed or by excessive flow rate.

Legionella

A series of bacteria, including legionella pneumophila, which can cause pneumonia-like illness called Legionnaires disease after the American Legion convention in Philadelphia where the disease first drew attention. These bacteria have been found growing in hard water scale and thrive below 140 degrees Fahrenheit in water heaters, showers, humidifiers, etc. Infection is obtained by inhalation.

Lime

The common name for calcium oxide (CaO); hydrated lime is calcium hydroxide, Ca(OH)2..

Lime Scale

Hard water scale containing a high percentage of calcium carbonate. Insoluble scale is commonly formed when water containing calcium carbonate is heated. It also forms in cold water but precipitates at a higher pH.

Lime Softening

Often used by municipalities for partial reduction of water hardness. After the addition of baked lime, soda ash is added to form an insoluble precipitate which is filtered from the water. This method leaves five or more grains of hardness.