Should I use reverse osmosis water?

Reverse osmosis forces water through a semi-permeable membrane, removing 95 to 99% of dissolved solids.

What it removes

Essentially everything — calcium, magnesium, bicarbonate, sodium, chlorine, nitrates, metals.

Output TDS is typically under 10 ppm.

Why that is a problem

Coffee needs minerals to extract. Magnesium and calcium bind to flavour compounds and carry them out of the grounds.

Brewed in RO water alone, coffee is thin, hollow and empty, with no sweetness and no body. It surprises people who assume pure water must be best.

The other problem

RO water is aggressive to metals. Low-mineral water is corrosive to copper and brass over time, and it will attack a boiler.

Many machines also use conductivity probes for water level, which fail with near-pure water — the machine believes the tank is empty.

The correct use

As a blank for recipe water. RO output plus a measured mineral dose gives you exact control, and it is what competition brewers do.

Blended. Many commercial installations blend RO output with a proportion of raw water to reach a target hardness.

Remineralisation cartridges

Many RO systems offer one. They add calcium and magnesium back after the membrane.

Convenient, and less precise than dosing yourself.

Is it worth installing at home

For a plumbed espresso machine in a hard-water area, yes — with remineralisation.

For jug brewing, a carbon filter and bottled water gets you most of the way for far less.