You’ll hear the quality of your espresso or coffee has a lot to do with the quality of the water you use to brew with - and that is very true. So it would seem logical that using the purest possible water would make the best cup. But you need to be careful of just how pure your water is.
Ultra Pure Water
Created using either distillation or reverse osmosis. These processes remove trace chemicals and dissolved solids including minerals. Some homeowners concerned with water quality have installed under-sink reverse osmosis systems.
But here’s what you need to know: Water is often called the universal solvent. It’s incredibly good at dissolving things. In fact, distilled and reverse osmosis water with near zero dissolved solids are such good solvents they can leach minerals out of metal pipes and boilers used in coffee and espresso equipment. This can lead to corrosion and eventual failure of those parts.
It’s a reason why distilled and reverse osmosis water is always handled in plastic piping and containers which unlike metals are not susceptible to the solvent power of ultra-pure water.
Due to it’s ability to leach metals and cause corrosion we do not recommend using distilled or reverse osmosis water in coffee and espresso equipment. We do however recommend using a water filter. These remove some, but not all dissolved minerals. So you’ll have less scale build-up but the filtered water will not be pure enough to cause damage to metal parts. Learn more about Water Filters.