How to Set the Right Water Hardness on Your Dishwasher

Getting the dishwasher water hardness setting right is one of those small jobs that makes a real difference to your wash results. Set it correctly and your dishwasher uses just the right amount of salt to soften the water flowing through it. Get it wrong and you can end up with cloudy glasses, drop marks and salt running out far quicker than it should.

If your glassware keeps coming out spotty or your dishes feel gritty, the water hardness setting is a good place to start before assuming the machine is faulty.

Why your dishwasher needs soft water in the first place

Dishwashers (and washing machines) work best in soft water. To deal with hard water, every dishwasher has a built-in water-softening system. This is where dishwasher salt comes in.

There's a common myth worth clearing up. People assume the salt softens the water directly, but that isn't how it works. Inside the salt chamber there's a special resin, and it's the resin that converts hard water into soft water. The salt's actual job is to clean and restore that resin as water periodically flows through the chamber. Because the salt regenerates the resin, the salt chamber is often called a regeneration unit.

The resin doesn't last forever, and it relies on dishwasher salt to keep regenerating. If you never top up the salt, the resin eventually gives up and stops working. From that point, any hard water entering the machine passes straight through without being softened, which is exactly when washing results start to suffer.

One quick note on salt itself: only use dishwasher salt. It's made specifically for the job, so don't be tempted to substitute table salt or any other kind.

Why the water hardness setting matters

The regeneration unit needs adjusting to match the hardness of your local water supply, because that setting controls how often the resin is regenerated. In other words, your water hardness setting directly decides how frequently the machine cleans the resin and how quickly your salt gets used up.

Here's how it plays out:

• Set the machine for very hard water and it regenerates the resin more often, so salt depletes quicker.
• Set it for soft water and the resin regenerates less frequently, so a tank of salt lasts longer.

The problem comes when the setting doesn't match your actual water. An incorrect setting can lead to poor washing results because too much salt ends up present in the machine. The tell-tale sign is small drop marks left on items after a cycle, and you'll usually spot it on glassware first.

How to find your local water hardness value

Before you adjust anything, it helps to know how hard your water actually is. Some high-end dishwashers ask you to type in an exact water hardness value rather than picking a rough level. If yours does, get that value from your local water authority, as they'll have the figure for your postcode.

Even if your machine only offers broad settings, knowing whether you're in a hard or soft water area takes the guesswork out of the choice.

How to adjust the dishwasher water hardness setting

The method depends on the age and model of your machine:

• Modern dishwashers let you adjust the water hardness using the controls on the front of the machine. Check your manual for the exact button sequence, as it varies between makes.
• High-end dishwashers may ask you to enter an exact value. Use the figure from your water authority for the most accurate result.

Once it's set to match your supply, the machine will regenerate the resin at the right interval and use salt at a sensible rate.

Don't rely on combined tablets if you have hard water

It's tempting to use 3-in-1 tablets, which bundle detergent, salt and rinse aid into one, and skip the separate salt altogether. That only really works in areas with perfect soft water.

If your water is hard and contains any limescale, relying on combined tablets alone isn't enough. You still need to add dishwasher salt separately to keep the resin doing its job. The salt in a combined tablet simply isn't designed to regenerate the resin in the same way.

Watch for the low-level warning light

Most dishwashers show a warning light on the front when either the salt or the rinse aid is running low. When it lights up, take it as your cue to top up rather than waiting for wash quality to drop off.

How to top up dishwasher salt

Replenishing the salt is straightforward:

1. Unscrew the salt chamber cap and add the salt. You'll find the cap at the base of the machine when you open the door, usually just to the left of the filter. If you bought your dishwasher new, it should have come with a funnel to make pouring the salt in easier.
2. Screw the cap back on firmly.
3. Run an empty quick wash. This rinses away any excess salt left inside the machine, which helps avoid those drop marks on your next proper load.

Still getting poor results? It may be a fault

If you've matched the water hardness setting to your supply, kept the salt topped up and run a quick wash, but the dishes are still coming out poorly, the problem could be a fault with the appliance rather than your settings.

That's where we can help. NAC engineers repair dishwashers of any make, and you can book a repair through our website or call us on 0333 016 9622. We quote a service charge up front that covers all labour, the callout and VAT where it applies. The only extra is for parts if any are needed, and we'll quote those separately before any work goes ahead. Any repair we carry out comes with a guarantee, with the length depending on the parts fitted and covered under our terms and conditions.

Not sure we cover your model? Take a look at the brands we repair and our service areas to check we're near you.