Water hardness in Graz
Tap water in Graz measures 16.0 °dH.
Austria classes that as hart, meaning hard. On the internationally comparable scale, from the WHO and the US Geological Survey, that is very hard.
This figure sits close to a band boundary. The band is a label rather than a property of the water: a routine re-measurement can move the same tap into the neighbouring band.
How hardness is classified
There is no European classification; each country sets its own bands. Here is how the country itself classifies it, and how the international scale compares:
How Austria classifies it
Internationally, from the WHO and the US Geological Survey
Does the figure apply at your address?
Not necessarily. The published figures for this city run from 15.0 °dH to 17.0 °dH, depending on the waterworks, the zone, or simply when the sample was taken. Which of them reaches a given address is a question only the utility can answer.
midpoint of the published 15-17 dH range, which straddles the boundary between Austrian hardness levels II and III
The figure for your address or postcode is available directly from Holding Graz — and it is often printed on the water bill too.
A hardness test strip from a chemist or hardware shop costs a few euros and settles it in a minute. That is also the only way to know what comes out of your own tap rather than what leaves the waterworks.
Setting an appliance
A dishwasher, washing machine or coffee machine that asks for a level from 1 to 4 wants 3 here.
That four-level scale is the one German detergent law used until 2007. The law moved to the three bands above; the dials did not.
The same figure on other scales
16.0 °dH · 28.6 °f · 2.85 mmol/l · 286 mg/L
Dishwashers and washing machines ask for hardness in different units depending on where they were sold: millimoles per litre in Germany, degrees in Austria and Switzerland, parts per million in Britain. It is one quantity read on four scales.
What it means day to day
Very hard water leaves a lot of limescale. Kettles, coffee machines and shower heads scale up markedly faster, detergent needs a higher dose, and anything with a heating element is worth descaling regularly.
Hard water is not a fault
Hardness is not a safety question. Hard water is fine to drink; it just leaves more limescale.
The calcium and magnesium that make water hard are the same minerals a diet needs, and drinking water counts towards the daily intake of both. The WHO reviewed how much in Calcium and magnesium in drinking-water.
A thin carbonate layer on the inside of a pipe also protects the metal underneath from corroding. Water softened to nothing is harder on plumbing, not easier.
The water is fine to drink either way: Is the tap water in Graz safe to drink?
How it compares
Of the 15 cities in Austria with a published figure here, Graz is the 6th hardest. The middle of the range sits at 12.6 °dH.
The softest is Innsbruck at 6.2 °dH, the hardest Linz at 19.5 °dH.
Where the figure comes from
Published by Holding Graz, which gives no measurement date.
The figure is total hardness, which counts every calcium and magnesium compound in the water. Some utilities also publish carbonate hardness, the part bound to carbonic acid, which is the share that forms limescale when the water is heated.