Total Dissolved Solids (TDS) is a common concern regarding drinking water quality. This measurement reflects the total concentration of inorganic salts, minerals, and metals dissolved in the water. TDS is a collective measure, not an identification of specific substances, so whether it is harmful depends entirely on what those dissolved solids are.
Defining Total Dissolved Solids
Total Dissolved Solids represents the combined mass of all substances dissolved in a water sample that pass through a two-micrometer filter. This concentration is typically expressed in parts per million (ppm) or milligrams per liter (mg/L). TDS is primarily composed of positively charged ions (calcium, magnesium, sodium, potassium) and negatively charged ions (chlorides, bicarbonates, sulfates).
Water is an excellent solvent, picking up minerals from natural sources as it moves through rock and soil. Human activities, including agricultural runoff, wastewater discharge, and urban runoff, also contribute to the overall TDS level. A TDS reading measures the total quantity of dissolved material, but it reveals nothing about the identity of the components. For example, a high reading could be due to harmless calcium and magnesium, or concerning heavy metals.
Health and Aesthetic Implications of TDS
The presence of dissolved solids impacts the aesthetic qualities of drinking water before posing a health threat. Water with high TDS often acquires a noticeable metallic, salty, or bitter taste, depending on the predominant ions present. Taste issues typically become apparent when the TDS level exceeds approximately 500 ppm.
Very high TDS levels can cause cloudiness and lead to scaling or mineral buildup on plumbing fixtures, pipes, and appliances. While minerals like calcium and magnesium are generally harmless, they contribute to water hardness, reducing the effectiveness of soaps and detergents. The World Health Organization suggests a maximum limit of 600 mg/L for drinking water palatability.
High TDS readings, especially those exceeding 1,000 ppm, indicate that the water quality warrants a closer look. At these elevated concentrations, there is an increased chance that the dissolved solids include harmful contaminants, such as nitrates, arsenic, or lead, which pose a direct health risk. Water supplies with extremely high TDS levels are generally considered unsuitable for consumption unless a comprehensive test confirms the safety of the specific components.
Testing and Mitigation Strategies
Consumers can easily measure the TDS level of their water using inexpensive, handheld electrical conductivity meters. These meters work because dissolved ions increase the water’s ability to conduct an electrical current, providing a quick estimate of the total dissolved content. However, these meters cannot identify specific contaminants, which is the most important factor for health.
If a home meter shows a high or rapidly changing TDS reading, a professional laboratory water test is recommended. Laboratory testing uses precise methods, such as gravimetry, to chemically analyze the water and identify the exact concentration of specific elements like heavy metals or nitrates. This professional analysis determines the true safety of the water supply.
To reduce high TDS, the most effective technologies are Reverse Osmosis (RO) and Distillation. RO systems force water through a semi-permeable membrane that blocks the dissolved solids, removing up to 99% of them. Distillation involves boiling the water and collecting the resulting steam, which leaves the dissolved solids behind. Standard filtration methods, such as carbon or sediment filters, are not designed to remove dissolved solids and will not significantly lower the TDS reading.