Total Dissolved Solids (TDS) measures the total concentration of inorganic salts and small amounts of organic matter dissolved in water. This measurement is a common indicator of overall water quality, often causing consumer concern about the taste, appearance, and safety of drinking water. Understanding the TDS level is important because it signals the presence of substances that affect both aesthetic qualities and, in some cases, health implications.
Understanding Total Dissolved Solids
Total Dissolved Solids are substances that pass through a filter with pores around two micrometers in size. The composition primarily consists of inorganic salts, including beneficial minerals such as calcium, magnesium, potassium, and sodium. These minerals are often present as cations and anions like chlorides, bicarbonates, and sulfates.
Dissolved solids originate from both natural geological processes and human activity. Natural sources include the weathering and erosion of rocks and soil, which introduces minerals into the water supply. Human sources include agricultural and urban runoff, wastewater discharges, and the use of road de-icing salts. TDS is measured by a meter, typically expressed in parts per million (ppm) or milligrams per liter (mg/L).
Establishing Safe Drinking Limits
The maximum allowable level of TDS in drinking water is generally treated as an aesthetic standard rather than a health-based one. The U.S. Environmental Protection Agency (EPA) established a Secondary Maximum Contaminant Level (SMCL) for TDS at 500 mg/L. This non-enforceable guideline addresses cosmetic and aesthetic effects, such as taste and staining, rather than immediate health risks.
The World Health Organization (WHO) offers a similar guideline, suggesting that a TDS level below 600 mg/L is acceptable for palatability. The EPA’s regulation is a secondary standard, distinct from primary standards that set legally enforceable limits for contaminants posing a direct health risk, like lead or arsenic. A high TDS reading often indicates the need for further testing for specific, harmful contaminants, but the number itself is not a direct measure of toxicity.
Health vs. Aesthetic Impacts of TDS Levels
The most common complaints about high TDS levels relate to aesthetic issues. Water with high dissolved solids, often exceeding the 500 mg/L guideline, can acquire a salty, metallic, or bitter taste, making it unpalatable. These solids can also cause staining on plumbing fixtures and a cloudy appearance in the water. High TDS can also lead to scale buildup in pipes and water-using appliances, reducing their efficiency and lifespan.
Health concerns related to TDS are generally indirect, depending on the specific substances measured. While the aggregate TDS number is not a direct health hazard, extremely high levels (e.g., above 1,000 mg/L) can concern specific populations. For example, high sodium content may affect individuals on a low-sodium diet, and high sulfate levels can have a laxative effect. High TDS can also indicate that harmful primary contaminants, such as nitrates or heavy metals, may be present and require separate testing.
Managing High TDS Levels in Household Water
For homeowners concerned about elevated TDS, the first step is to have the water professionally tested to identify the specific dissolved solids present. This analysis is necessary because the presence of certain minerals may only require a water softener, rather than a full filtration system. Water softeners address hard water minerals like calcium and magnesium through an ion exchange process, replacing them with sodium or potassium, which reduces a portion of the overall TDS.
For comprehensive reduction, water treatment methods like reverse osmosis (RO) systems are highly effective. RO systems force water through a semipermeable membrane, removing up to 99% of dissolved solids and significantly lowering the TDS level. Distillation and deionization are other methods that achieve a similar high-purity result.