Total Dissolved Solids (TDS) is a measure of all inorganic and organic substances dissolved in water, expressed in parts per million (ppm). This includes minerals like calcium and magnesium, salts, and even some metals. While often used as a quick water quality check, understanding TDS requires looking beyond a single number.
TDS matters in specific scenarios. In commercial settings like coffee shops or breweries, consistent mineral content (a component of TDS) is crucial for perfect extraction and taste. For aquarium owners, specific TDS levels are vital for sensitive aquatic life. In industrial applications, high TDS can cause damaging scale buildup in equipment. It’s also a useful, though non-specific, indicator for checking the effectiveness of reverse osmosis (RO) or distillation systems—a rising TDS reading signals a filter change is due.
However, the common belief that lower TDS always means better water is a dangerous misconception. Extremely low TDS, often produced by some filtration systems, results in “aggressive” water that readily leaches metals from pipes, potentially increasing lead or copper exposure. Furthermore, TDS tells you nothing about what the solids actually are. Water with 200 ppm of healthy calcium is vastly different from water with 200 ppm of harmful nitrates or heavy metals, yet the TDS meter reads the same.
Ultimately, TDS is a measure of purity, not safety. It cannot identify specific contaminants. A low reading doesn’t guarantee water is free of dangerous bacteria, pesticides, or VOCs. Conversely, a moderately high reading often reflects beneficial minerals that contribute to taste and health. Before chasing a low TDS, identify your local contaminants and choose a filter that targets them, understanding that preserving some natural minerals is typically a good thing.
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