What water hardness is, and why it's not just about looks

Water hardness measures its calcium and magnesium content, which water accumulates as it passes through different types of soil. It's expressed in French degrees (°F): one degree equals 10 mg of calcium carbonate per litre of water. Water is considered soft up to about 15°F and becomes "very hard" above 30°F.

The difference between soft and hard water isn't just white streaks on dishes. Limescale builds up inside pipes, taps and, especially, water heaters, causing blockages, breakdowns, higher energy use and a shorter equipment lifespan.

Why water varies so much from one district to another in Geneva

Here's a point many owners don't know: water hardness in the canton of Geneva doesn't depend on the canton as a whole, but on the specific supply zone, and the gap can be considerable.

Geneva's water utility (SIG) distinguishes several zones. Water from Lake Geneva is the softest, around 13–14°F. Water mixed with groundwater from the Allondon stays soft to moderately hard, between 13 and 22°F. But where the network draws on the Genevois groundwater, hardness rises to 18–21°F — moderately hard, at times limescale-heavy water. Communes supplied by this groundwater, along with certain districts such as Carouge or Chêne-Bourg, are therefore the most affected by limescale. Two nearby addresses can show markedly different readings, depending on which branch of the network they're connected to.

The good news: water in Geneva is drinkable and of very good sanitary quality regardless of its hardness — it's regularly tested to strict Swiss standards. Hardness affects equipment and comfort, not the safety of the tap water.

How often to descale your water heater depending on hardness

Geneva's official recommendation gives a clear benchmark for how often to descale your water heater based on the hardness of the water in your zone. At 26–40°F, it's advisable to descale the water heater after five years. With softer water, between 10 and 25°F, descaling every ten years is enough.

In practice, this means that before planning your boiler's maintenance, it's worth finding out the exact hardness value for your address — it strongly influences how often and how thoroughly your equipment needs care.

How limescale affects plumbing and appliances

Limescale affects almost everything in contact with hot water. Tap and showerhead aerators clog up, and the flow becomes uneven. Water heaters lose efficiency because of scale on the heating element, leading to higher energy consumption. Appliances (washing machines, dishwashers) fail sooner because of deposits. On surfaces — shower screens, sinks, dishes — characteristic white marks appear.

What to do: diagnosis, not a one-size-fits-all solution

It's important to resist the temptation to buy a filter "just in case." The right solution depends on the hardness specific to your water, how you use it and your budget — and should be based on an on-site diagnosis, not general recommendations.

The first step is finding out the exact hardness value for your address: this information is available through your water supplier's customer portal, or can be checked on site with test strips. The second step is assessing the visible signs in the home: noticeable scale, clogged aerators, reduced pressure. The third is deciding on maintenance or the installation of softening equipment based on that data, rather than generic "rule of thumb" advice.

One point worth understanding: point-of-use filtration improves taste and odour but doesn't change the water's hardness itself — that requires solutions at the point where water enters the home.

How SmartHaus Swiss approaches hard water

We don't sell the same solution to everyone. When installing or servicing water heaters, taps and hot water systems, we take into account the water hardness specific to your zone and tailor the maintenance schedule, and equipment where needed, to your actual situation. The regular preventive descaling of water heaters we carry out extends equipment life and maintains both its energy efficiency and a safe water temperature.

Frequently asked questions

How do I find out the water hardness at my address?

The exact value is available through your water supplier's customer portal, or can be measured on site with test strips.

Is hard water dangerous for health?

No, water in Geneva is drinkable and tested to strict standards regardless of its hardness. Hardness affects equipment and comfort, not the safety of the water.

How often should a water heater be descaled?

At 26–40°F, roughly every five years; at 10–25°F, every ten years. The exact interval depends on the hardness specific to your zone.

Is water hardness the same across all of Geneva?

No, it can vary noticeably even between neighbouring addresses, depending on which branch of the supply network they're connected to.

Does everyone need a water softener?

No. The decision should be based on a diagnosis of your specific address and water usage, not a default choice.

Hardness values are based on Geneva's official water supply zones and may differ in other communes and cantons, and change over time. The exact value for your address should be checked with your local water supplier.