Bob Lowry Breaks Down TDS in Pool Water
Total Dissolved Solids (TDS) is one of the most ignored numbers in pool water chemistry, even though it quietly influences how water behaves. TDS simply means the total amount of dissolved material in the water, measured in parts per million, and it is not the same as visible debris or suspended solids. Modern pool service pros usually measure TDS with a digital meter that reads conductivity and converts that to a ppm estimate. That convenience is why it exists, because the old-school “total dissolved residue” method required evaporating a carefully measured sample and weighing what was left. The key takeaway for pool maintenance is that TDS rises as you add chemicals over time, and that rising baseline changes the way your test results and balance calculations perform. A practical way to think about TDS is the “kettle scale” analogy: keep boiling water away and you eventually see what was dissolved all along. In pools, the biggest contributors are often chloride and sodium. Every time...