The kettle furs up in three weeks. The shower head loses half its holes. The boiler makes a noise it did not make last winter. None of this is a fault in the flat. It is calcium, and on this coast there is plenty of it. Here is what the numbers mean, who pays when something breaks, and which fixes are worth the money in a rented home.
Hardness is measured in milligrams of calcium carbonate per litre, or in French degrees, where one degree is 10 mg/L. Below 60 mg/L is soft, 60–120 is moderately hard, 120–180 is hard, and above 180 is very hard. Barcelona city sits between roughly 186 and 329 mg/L depending on the supply zone and the sampling date, which puts most of the city in the hard to very hard band. Coastal Catalonia as a whole often runs 250–400 mg/L.
The Maresme is not one number. Arenys de Mar has published around 158 mg/L, which is only moderately hard. Towns drawing from different wells or buying water from Aigües de Barcelona can be well above that, and a hillside urbanización on its own tank is a separate story. Ask the supplier, or the town hall, for the hardness of the address you are considering. It takes one email and it explains a lot about the boiler.
A millimetre of scale on a heating surface is usually quoted as a 7–10% loss of efficiency. In a flat with an old gas boiler that difference shows up as €60–120 over a winter. A descaling service costs €80–150; a new boiler for a 100 m² flat costs €1,500–3,000 installed. That gap is why the boiler is the only item on this list worth arguing about.
Article 21 of the LAU says the landlord must keep the dwelling fit for its purpose and cannot pass the cost of necessary repairs into the rent. A boiler that no longer produces hot water is a habitability problem, and a service or repair is on the owner. A kettle, a shower head or a coffee machine is yours. The grey zone is a boiler that still works but has never been serviced: the owner will call it maintenance, you will call it neglect. Photos, a technician's report and a polite burofax settle it faster than an argument on the phone.
Do not stop paying rent to make the point. Withholding rent turns a repair request into an arrears case, and in Spain that is a much worse position. Pay, document, ask in writing, and keep the receipts for anything you bought to cope, such as a descaler or bottled water.
In a rental, a softener is a fixed installation and needs the owner's written consent under article 23, plus somewhere to put it. Some owners will split the cost because it protects their boiler. Ask for that in an annex that also says who removes it, and who fills the holes, when you leave.
Soak the shower head in vinegar or citric acid once a month, ten minutes of work. Wipe the glass after every shower with a squeegee, which is €8 and does more than any spray. Keep the dishwasher salt topped up even if the tablets claim to include it. Run a descaling cycle on the washing machine every two months at 60 °C with citric acid. And leave the boiler hot water at 60 °C, not lower, because the savings from 50 °C are smaller than the legionella risk.
Bottled water is the other habit. A 1.5 litre bottle costs €0.25–0.40, a family of four drinks 8–10 litres a day, and that is €25–40 a month plus the plastic. A jug filter pays for itself in the first month if you only care about taste.
Ask for the hardness at the address, the age and model of the boiler, the date of its last service and whether there is a softener and who maintains it. Then look under the sink: a leaking filter housing or a salt-stained floor tells you more than the answer. In a Maresme house with its own tank, ask when the tank was last cleaned and whether the water is treated.
Tell us the town and the age of the house. We know which Maresme urbanizaciones are on their own supply, which owners keep service records, and which boilers are living on borrowed time.
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