![]() The pH scale is logarithmic, which means that each step on the pH scale represents a ten-fold change in acidity. Pure water would have a pH of 7.0, but water sources and precipitation tends to be slightly acidic, due to contaminants that are in the water. Water with a low pH is said to be acidic, and water with a high pH is basic, or alkaline. The pH scale, as shown below, ranges from 0 to 14, with 7.0 being neutral. The pH level is a measurement of the activity of the hydrogen atom, because the hydrogen activity is a good representation of the acidity or alkalinity of the water. The pH value of a water source is a measure of its acidity or alkalinity. For more information about reverse osmosis, see the Ultrafiltration, Nanofiltration and Reverse Osmosis fact sheet. The mineral bed also increases the pH and decreases the corrosive potential of the water. It also removes healthy minerals, such as calcium and magnesium, and ideally such water should be filtered through a magnesium and calcium mineral bed to add the minerals to the water. Reverse osmosis removes virtually all dissolved substances, including many harmful minerals, such as salt and lead. Water treatment facilities can use reverse osmosis to remove the dissolved solids in the water that are responsible for elevated TDS levels. How Can Water Treatment Facilities Remove TDS? The United States guideline for TDS is also 500 parts per million. 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 do. In the United States, substances that are health-based have Maximum Contaminant Levels (MCLs), and are enforceable by law. 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. However, since the Canadian guidelines are not enforceable, each province is free to choose whether or not they will follow the guidelines. ![]() The Canadian guideline for TDS is less than 500 milligrams per litre (which is the same as 500 parts per million). However, substances that are not considered dangerous at their MAC, such as TDS, are given an aesthetic objective in the Guidelines. In Canada, substances that are considered to be dangerous in high amounts are listed as Maximum Acceptable Concentrations (MACs) in the Canadian Guidelines for Drinking Water Quality. This is especially true when the excessive dissolved solids are added to the water as human pollution, through runoff and wastewater discharges. 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 iron, manganese, sulfate, bromide and arsenic, can also be present in the water. In a study by the World Health Organization, a panel of tasters came to the following conclusions about the preferable level of TDS in water: Most people think of TDS as being an aesthetic factor. While the United States set legal standards for many harmful substances, TDS, along with other contaminants that cause aesthetic, cosmetic and technical effects, has only a guideline. 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. In fact, many people buy mineral water, which has naturally elevated levels of dissolved solids. What Happens to the Water When the TDS Level is High?Īlone, a high concentration of dissolved solids is usually not a health hazard. 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. These minerals can also come from human activities. The water in the Prairie provinces tends to have high levels of dissolved solids, because of high amounts of calcium and magnesium in the ground. 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. These minerals can originate from a number of sources, both natural and as a result of human activities. How do These Solids End Up Dissolved in Water? Cations are positively charged ions and anions are negatively charged ions. Common inorganic salts that can be found in water include calcium, magnesium, potassium and sodium, which are all cations, and carbonates, nitrates, bicarbonates, chlorides and sulfates, which are all anions. TDS is made up of inorganic salts, as well as a small amount of organic matter. TDS stands for total dissolved solids, and represents the total concentration of dissolved substances in water.
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