Water quality is a growing concern for consumers who are becoming more aware of what is dissolved in their drinking supply. The purity of water is frequently gauged by a simple measurement that indicates the total amount of dissolved matter present. This metric, often expressed in parts per million (PPM), provides a rapid assessment of the water’s composition. Understanding this measurement is the first step in evaluating and improving the water that flows into your glass.
Understanding Total Dissolved Solids
The primary metric used to quantify the substances in water is Total Dissolved Solids (TDS). This represents the combined concentration of all inorganic salts, organic substances, and other matter dissolved in the water. The unit of measurement for TDS is typically parts per million (PPM), which is equivalent to milligrams per liter (mg/L).
Consumers often measure this value using a simple handheld TDS meter. The meter estimates the TDS concentration by measuring the water’s electrical conductivity (EC). Dissolved substances, such as salts and minerals, create charged ions that allow the water to conduct electricity, and the meter converts this conductivity into a TDS reading.
Establishing the “Good” PPM Range
Determining a “good” PPM for drinking water involves considering both regulatory guidelines and consumer preferences. The U.S. Environmental Protection Agency (EPA) established a Secondary Maximum Contaminant Level (SMCL) for TDS at 500 PPM. This is a non-enforceable guideline focused on the aesthetic quality of the water, addressing taste, odor, and appearance, rather than health risks.
Water with TDS levels above 500 PPM may cause excessive scaling in pipes and appliances, and often has an unpleasant salty or metallic taste. Conversely, water under 50 PPM often tastes “flat” because it lacks the dissolved minerals that contribute to flavor. For optimal taste and palatability, many experts suggest an ideal range between 50 PPM and 300 PPM. This range balances cleanliness with retaining enough natural minerals for a refreshing taste.
What Constitutes the Dissolved Solids Count?
The total number reflected by a TDS reading is a composite of many different substances, including both beneficial minerals and undesirable contaminants. The majority of the count comes from naturally present inorganic salts and essential minerals. These beneficial components include positively charged ions like calcium, magnesium, sodium, and potassium, and negatively charged ions such as bicarbonates, chlorides, and sulfates.
These substances dissolve as water travels through the environment, leaching from rocks and soil. However, the TDS count can also include undesirable substances like heavy metals, industrial pollutants, and organic matter from agricultural or urban runoff. A high TDS reading is a general indicator that requires further investigation, as it does not differentiate between harmless and potentially hazardous components.
Health Implications vs. Taste and Aesthetics
The TDS level is not a direct measure of water safety or a comprehensive health assessment. High TDS primarily affects the water’s aesthetic qualities, leading to issues like a bitter or salty taste, cloudiness, or staining of fixtures and laundry. Above 500 PPM, the water can also cause technical problems, such as mineral buildup that reduces the efficiency and lifespan of hot water heaters and other household appliances.
A low TDS reading does not guarantee the water is free of harmful contaminants. Certain dangerous substances can be present at concentrations too low to significantly impact the overall PPM. For instance, trace heavy metals like lead or arsenic are measured in parts per billion and barely register on a TDS meter, yet they pose significant health risks. Therefore, TDS is a useful starting point but cannot replace comprehensive laboratory testing for specific toxins or microbiological contaminants.
Adjusting TDS Levels Through Filtration
For consumers looking to modify their water’s TDS level, various filtration methods offer different levels of reduction. Reverse Osmosis (RO) is the most effective technology for drastically reducing TDS, often removing up to 97% of dissolved inorganic solids. The RO system forces water through a semi-permeable membrane, separating water molecules from almost all dissolved salts and minerals, yielding a very low PPM.
Distillation is also highly effective at reducing TDS, as the process involves boiling the water and collecting the resulting pure steam, leaving all solid matter behind. By contrast, activated carbon filters are commonly used for improving taste and odor but are not designed to remove inorganic dissolved solids. While they excel at removing chlorine and organic compounds, carbon filters typically only reduce the TDS level by a negligible 10 to 15%.