This fix needs no special products: mix bottled drinking water with de-ionised water to bring the minerals into range. De-ionised water is near zero minerals, so a 1:1 mix halves every value on the label, and more de-ionised pushes them lower. This only works when the bottle’s minerals are already in the right proportions – dilution lowers the concentration, it does not fix the balance.

Pick a water whose mineral ratios roughly match the targets table below, dilute until the hardness lands in range, and verify the first batch with a test kit. The mix is only right when the test says so.

A resin softener on the tank hose, like the LELIT Water Softener Filters, or a filter pitcher filled with bottled water, not tap.

The bottle gives you a chlorine-free starting point with a printed analysis; the filters reduces the hardness the last step into range. Replace the cartridge on schedule.

Tap water through an activated carbon filter that strips chlorine and sediment and a softener filter that takes hardness partway down.

Chlorine has to go either way: it ruins the taste and attacks seals and gaskets.

What this filter cannot do is regulate hardness, it removes a fixed amount from whatever your tap happens to be that month.

A plumbed-in filter with a bypass you tune: either a single cartridge that combines sediment, carbon and ion exchange (BWT Bestmax, Everpure Claris Ultra) or an RO system with remineralisation.

The bypass dial is the point, instead of removing a fixed amount, you set how much mineral content passes through and dial the output into the target range.

Set it once, verify with a test, recheck when the season changes.

Start from RO, distilled or de-ionised water at near zero minerals, then add back an exact measured dose with mineral concentrates like APAX LAB minerals.

Nothing is left to the tap, the season, or the filter’s mood: the recipe is the water.

This is how competition baristas do it, and the only method where two brews a year apart taste identical.