TDS means total dissolved solids which represents the total concentration of dissolved substances in Packaged Drinking water. It is made up of inorganic salts, as well as less amount of organic material. Common inorganic salts that can be found in water must include calcium, magnesium, potassium and sodium, which are cations, carbonates, nitrates, bicarbonates, chlorides and sulfates, which are all anions. Cations are positively charged ions and anions are negatively charged ions.
HOW DO THESE SOLIDS END UP DISSOLVED IN WATER?
These minerals can originate from a number of sources, both natural and as a result of human activities. Mineral springs contain water with high levels of dissolved solids, because the water has flowed through a region where the rocks have a high salt content. The water in prairie provinces tends to have high levels of dissolved solids, because of high amount of calcium and magnesium in the ground.
These minerals can also come from human activities. Agricultural and urban runoff can carry excess minerals into water sources, as can wastewater discharges, industrial wastewater and salt that is used to de-ice roads.
WHAT HAPPENS TO THE Packaged Drinking WATER WHEN THE TDS LEVEL IS HIGH?
Alone, a high concentration of dissolved solids is usually not a health hazard. In fact, many people buy mineral water, which has naturally elevated levels of dissolved solids. The United States Environmental Protection Agency (EPA), which is responsible for drinking water regulations in the United States, includes TDS as a secondary standard, meaning that it is a voluntary guideline in the United States.
Increased concentration of dissolved solids can also have technical effects. Dissolved solids can produce hard water, which leaves deposits and films on fixtures, and on the inside of hot water pipes and boilers. Soaps and detergents do not produce as much lather with hard water as with soft water. As well, high number of dissolved solids can stain household fixtures, corrode pipes, and have a metallic taste.
Hard water causes water filters to wear out sooner, because of the amount of minerals in the water. The picture below was taken near the mammoth hot springs, in Yellowstone national park, and shows the effect that water with high concentration of minerals can have on the landscape. The same minerals that are deposited on these rocks can cause problems when they build up in pipes and fixtures.
However, while TDS itself may be only an aesthetic and technical factor, a high concentration of TDS is an indicator that harmful contaminants, such as manganese, iron, sulfate, bromide and arsenic, can also be present in the water. This is especially true when the excessive dissolved solids are added to the water as human pollution, through runoff and wastewater discharges.
WHAT ARE THE GUIDELINES FOR TDS?
In Canada, substances that are considered to be dangerous in high amounts are listed as Maximum Acceptable Concentrations (MACs) in the Canadian Guidelines for Packaged Drinking Water Quality. However, substances that are not considered dangerous at their MAC, such as TDS, are given an aesthetic objective in the Guidelines. The Canadian guideline for TDS is less than 500 milligrams per liter (which is the same as 500 parts per million).
However, since the Canadian guidelines are not enforceable, each province is free to choose whether or not they will follow the guidelines. Saskatchewan has water that naturally contains high concentrations of TDS, so the province has chosen to not follow the Canadian guideline of 500 parts per million, and to implement its own guideline of 1,500 parts per million.
In the United States, substances that are health-based have Maximum Contaminant Levels (MCLs), and are enforceable by law. However, TDS, and other substances that are considered aesthetic, are given Secondary Maximum Contaminant Levels (SMCLs),
but are not enforced, because they do not pose as great a health risk as the primary contaminants does. The United States guideline for TDS is also 500 parts per million.