Tap, filtered, bottled and softened water compared

Water for an espresso machine comes in five common types: tap, filtered, bottled, reverse osmosis (RO) or distilled, and softened. Each changes the dissolved minerals in a different way. Does your maker's manual allow it? That's the test.

Tap water

It's whatever your supplier sends, and the hardness varies by place. Breville says that depending on the machine and the water hardness, tap water may work great¹. Decent Espresso says any tap water should be filtered before use in its machine².

Filtered water

"Filtered" covers many devices, so ask what the filter removes. Decent says carbon block or media filters don't appreciably change how much scale the water will deposit. They don't significantly affect dissolved calcium and magnesium².

Some machines take a filter made for them. Breville says replacing that filter as recommended can help reduce mineral buildup¹. It also lists heavily filtered water that removes nearly all minerals among the types to avoid¹.

Bottled water

Labels differ, and so do the rules behind them. Wikipedia describes mineral water as coming from a protected underground source, with no minerals added³. Spring water comes from an underground formation where water flows naturally to the surface³.

Wikipedia says bottled mineral water usually contains higher TDS than tap water⁴. That's why a bottle isn't automatically a gentle choice for a machine. Check the label's mineral figures against your manual.

Breville names bottled spring water and mineral water as options where tap water is too hard for a model¹. Rules on how bottled water is named differ by country. Wikipedia notes that Canada has two categories, spring or mineral water and other water³. The European Union treats mineral water and spring water as its two main types³.

Reverse osmosis and distilled water

Distilled water has been purified by boiling it into vapor and condensing it back into liquid in a separate container⁵. Wikipedia lists distillation and reverse osmosis as the two most widely used non-chemical methods of water softening⁶.

Here the makers split. Breville says to avoid water with little or no mineral content. It says RO water may be suitable for applicable models only if some mineral content has been added back¹. It also tells readers not to assume highly purified water is better for an espresso machine¹.

Decent Espresso says its machines are designed to safely use unremineralized reverse osmosis water². Same water. Opposite advice. Each applies to that maker's own machines.

Softened water

A household softener is a different thing from a filter. Common home units use ion-exchange resin. Ion-exchange devices reduce hardness by replacing calcium and magnesium with sodium or potassium ions⁶.

Decent says typical salt-based or potassium chloride-based softeners don't significantly increase chloride levels². It warns, though, that chloride greatly increases corrosion risk in its machines². Is softened water allowed? Only your own manual can say. If it's silent, ask the maker.

A short comparison

For each maker's full wording, see the manuals page. Timing and products are on the descaling page.