Drinking Water Glossary

ALGAECIDE - Algae are microscopic single or multi-celled organisms commonly found in surface water. They produce their own food through photosynthesis. Excessive algae growth may cause water to have undesirable odor or taste. Algaecides, such as chlorine dioxide, help kill and remove algae.

ALKALINITY - The capacity of a water to neutralize a strong acid, usually to pH of 4.2. Surface water from the Nueces River typically has a pH of 7.9 while Lake Texana water has a pH of 8.0. The target for delivered drinking water is a pH of 7.6 to 7.8.

BRACKISH WATER - Typically groundwater that is not considered freshwater or saltwater but is in between. Brackish groundwater is defined as groundwater containing between 1,000 and 10,000 milligrams per liter (mg/L) total dissolved solids (TDS). Texas has a tremendous resource in brackish groundwater including areas in San Patricio County.

CAUSTIC - Chemical such as sodium hydroxide used to balance pH.

CHLORAMINES - Disinfectants formed by the reaction of ammonia with chlorine.

CHLORINE - A heavy, greenish-yellow gas with a pungent odor. It is added to water for disinfection and in the oxidation of compound impurities in water.

CHLORINE RESIDUAL - Amount of chlorine remaining after reaction with things in the water. It is important to maintain chlorine residual throughout the water distribution system.

COAGULATION - Chemical neutralization of suspended and dissolved particles in the water. Alum is added as a coagulant to cause particles to clot together.

COLIFORMS - Bacteria used as an indicator of microbial contamination in water. While not disease-causing organisms themselves, they are often found in association with other microbes capable of causing disease. Coliform bacteria are more hardy than many disease-causing organisms; therefore, their absence from water is a good indication that the water is safe to drink.

CRYPTOSPORIDIUM - A microorganism commonly found in rivers which is highly resistant to disinfection and can cause serious illness in some people.

DESALINATION - The removal of salt from seawater or brackish water to produce drinking water.

DISINFECTANT - A chemical (commonly chlorine, chloramine or ozone) or physical process like ultraviolet light that kills microorganisms such as bacteria, viruses and protozoa.

DISSOLVED SOLIDS - Solids in water that cannot be removed by filtration.

DISTRIBUTION SYSTEM - A network of pumps, tanks and pipes leading from a treatment plant to a customer's water meter.

FILTRATION - Removal of suspended material from water by filter systems.

FLOCCULATION - When alum and other chemicals are added to water it causes particles to clump together forming a "floc" of larger particles. The combined weight of the particles and the alum become heavy enough to sink to the bottom during sedimentation.

MEMBRANE - A thin barrier that allows some compounds or liquids to pass through but stops others. SPMWD uses cartridges of hollow fiber membrane straws in the Plant C microfiltration system.

POTABLE WATER - Water that is safe for drinking and cooking.

pH - The value that determines if a substance is acid, neutral or basic, calculated from the number of hydrogen ions present. It is measured on a scale of 0 to 14 on which 7 is considered neutral. Values below 7 indicate acidic and values above 7 indicate that it is basic.

PRODUCT OR FINISHED WATER - Water that has been treated and is ready to be delivered to customers.

RAW WATER - Water in its natural state, prior to any treatment for drinking or industrial use.

REVERSE OSMOSIS - The reversed osmosis (RO) process uses a semi-permeable membrane to separate and remove dissolved solids, organics and other material from water. It requires pressure to force pure water across a membrane, leaving the impurities behind.

SEDIMENTATION - Process of settling of floc or suspended matter in a sedimentation basin. The resulting sludge is periodically removed for land application.

TOTAL DISSOLVED SOLIDS (TDS) - A measure of the total level of dissolved solids including minerals, salts or metals in water. It comes primarily from natural sources. It is an indicator of general water quality.

TOTAL ORGANIC CARBON (TOC) - The amount of carbon in an organic compound that is often used as a non-specific indicator of water quality.

TURBIDITY - The cloudy appearance of water caused by the presence of tiny particles. Turbidity has no health effect but can interfere with disinfection. It may indicate the presence of disease-causing organisms that can cause symptoms such as nausea, diarrhea and associated headaches.

WATERSHED - The land area from which water drains into a river or reservoir. See the watershed map at Where Our Water Comes From.