Total dissolved solids (TDS) is measured as a volume of water with the unit milligrams per liter (mg/L), otherwise known as parts per million (ppm). According to the EPA secondary drinking water regulations, 500 ppm is the recommended maximum amount of TDS for your drinking water. Any measurement higher than 1000 ppm is an unsafe level of TDS. If the level exceeds 2000 ppm, then a filtration system may be unable to properly filter TDS.
TDS reading will come from anything in the water that is dissolved, and not seen, for instance, Calcium, Magnesium, Silica, Iron, Fluoride, and many others. The only water that would register at 0 or near 0 would be distilled water.
If you are concerned with TDS levels, a reverse osmosis system is needed to reduce the levels in the water. Please reach out to a SpringWell support member with any questions!