What is TDS?
TDS stands for total dissolved solids and is a measurement of inorganic and organic substances that are dissolved in water. Technically speaking , dissolved solids are defined as solids that can be passed through a sieve size of two micrometers. When measuring TDS in drinking water it is typically made up of mostly in-organics such as chloride, sulfate, calcium, magnesium, potassium, carbonates and bicarbonates.
What do results mean? Is it regulated?
TDS is regulated under the EPA’s Safe Drinking Water Act as a secondary contaminant at a level of 500 parts per million. Secondary contaminants are defined as those that cause aesthetic problems like taste, odor and appearance. While a high TDS level may not have health implications it is important to determine what is making up the TDS levels. There are elements such as lead and arsenic which are harmful to your health and can contribute to the TDS levels, but these are typically found in much lower levels. Since TDS does affect the taste, keep in mind that some people prefer water that has some level of TDS.
Testing for TDS
TDS is commonly measured in drinking water as an indicator of general quality. TDS can be measured in two ways: gravimetrically or by electrical conductivity. The gravimetric method is the more accurate method and involves evaporating the water from the sample and weighing the residue using a precision analytical balance. This method is time consuming and can be inaccurate if the TDS is made up of low boiling point organics which are easily evaporated along with the water. The electrically conductivity is directly related to the amount of dissolved ionized solids, so measuring the conductivity of the water gives an approximation of the TDS level.
Measuring by conductivity is done using a meter which measures the electrical conductance and will get you within 10 percent of the true TDS level.
Water Treatment Options
TDS can be reduced in a variety of ways depending on what is actually making up the TDS. The most common ways to remove dissolved solids is through reverse osmosis or distillation. Otherwise you can utilize treatment options specifically geared toward removing the actual contaminant causing the TDS in the water.