Total dissolved solids is a measure of everything dissolved in your water that isn't pure water, including calcium, magnesium, sodium, chloride, sulfate, nitrate, and trace metals. It's reported in parts per million and read quickly with an inexpensive TDS meter, which measures electrical conductivity and estimates the dissolved content from it. A higher number means more dissolved material. It's a useful overall snapshot, but it tells you the quantity of dissolved solids, not which specific ones are present.
That distinction matters because TDS isn't by itself a safety measure. Water at 50 ppm could carry a dangerous contaminant, while water at 500 ppm might be perfectly healthy, just mineral-rich. The EPA sets 500 ppm as a secondary standard, meaning it's about taste, odor, and appearance rather than health. High-TDS water often tastes salty, metallic, or bitter and speeds up scale. Very low TDS water can taste flat. So TDS matters most as an indicator and a taste predictor, not a contamination verdict.
In Arizona, TDS runs high for natural reasons. The Colorado and Salt River supplies pick up dissolved minerals as they flow over and through mineral-rich terrain, and groundwater adds more. Readings of 400-700 ppm are common at the tap, and some well water tops 1,000 ppm. This is the same mineral content that makes the water very hard, so high TDS and hard water tend to travel together here. It's why fixtures spot and scale and why a lot of homeowners go after treatment.
If your TDS is high and you want it lower, reverse osmosis is the standard fix, removing most dissolved solids and typically dropping a 500 ppm supply to under 50 ppm at the tap. A water softener doesn't lower TDS. It swaps calcium and magnesium for sodium, keeping the dissolved load about the same while cutting scale. Carbon filters and standard cartridge filters leave TDS pretty much unchanged too. So matching the tool to the goal matters: softening for scale, RO for TDS.
For most households, the right move is to measure rather than guess. A handheld TDS meter gives you a baseline in seconds, and if the number's high, a full water test identifies which solids dominate so you treat the right problem. Chasing the lowest possible TDS isn't the goal, since some mineral content improves taste. What you're after is water that tastes good, doesn't scale aggressively, and stays within limits for any contaminant of concern.