Quick Answer
TDS is total dissolved solids — a measure of dissolved minerals, salts, and other substances in water, reported in parts per million (ppm) or mg/L. A high TDS number tells you water has more dissolved material, but it does not tell you which substances they are or whether they are harmful.
Problem
TDS meters and test kits show a number, but most people do not know what it means — or that TDS alone cannot identify specific contaminants.
Product Recommendation
For shower water, TDS is not the same concern as chlorine or chloramine. ZOOSHEN filters target shower-water experience; a softener addresses hardness separately. See /water-science/water-hardness-units to distinguish the two.