The minerals in overly hard water can wreak havoc on an Espresso machine causing scale buildup in the boiler & on the heating element, steam wand & valves, as well as any part the water touches. At the same time, water that is too pure, too soft, doesn't make great Espresso either. Better to know what's there, rather than guess, and this simple to use Hanna TDS meter will help you fine tune your system. This is a Hanna Instruments TDS-1 Meter with automatic temperature compensation. This hand held instrument, made in Italy, measures total dissolved solids in water. Gives simple, clear readout of Parts Per Million (PPM) of 0 to 999, effective temperature range is 5 to 50 C. Comes with screwdriver for calibration, operating instructions, and protective plastic storage case. Meter measures 6" long. We, as many others, use a pour through cartridge filter water pitcher, and this meter has paid for itself in savings on water filter cartridges alone! Included are 2 packets (20ml each) of TDS Meter Calibration Solution from Hanna. You should calibrate the TDS meter before your first use.