What is ideal water TDS for espresso?

The Specialty Coffee Association recommends 75–150 mg/L (ppm) TDS for brewing water, with 150 ppm being the sweet spot many home baristas target. Water with TDS under 50 ppm (like most distilled water) is too soft and corrosive. Water over 200–250 ppm causes rapid scale buildup. You can measure TDS with a cheap TDS meter ($10–$15 on Amazon) and adjust by mixing tap water with distilled water to hit your target range.