Take the lower basket out of an Asko dishwasher and look at the floor of the tub. Next to the filters there is a screw cap, usually large and plastic. Under it is a reservoir that holds regenerating salt for a built-in ion-exchange water softener. The machine softens its own incoming water before it washes with it. That is standard on European dishwashers and unfamiliar on most American ones, which is why plenty of Asko owners find the cap after several years and assume it is a drain plug.
What the Softener Is Doing
Hard water carries dissolved calcium and magnesium. Heated, those deposit as scale on the heating element and as a haze on glass. The softener passes incoming water through a resin bed that swaps the hardness minerals for sodium, and periodically flushes the resin clean with a strong brine drawn from the salt reservoir. Run the machine with an empty reservoir in a hard-water area and the resin stops regenerating: scale builds on the element, glasses cloud, and the film on plastics never quite rinses away.
Use the Right Salt
The reservoir takes coarse dishwasher regenerating salt and nothing else. Table salt, rock salt sold for cooking and water-softener pellets meant for a whole-house system are not interchangeable with it; fine salt and additives cake and can damage the softener. Salt is also not rinse aid and not detergent, and the three go in three different places. If you are unsure which compartment you are looking at, the salt cap is inside the tub in the floor; the detergent and rinse aid compartments are in the inner door.
Filling It Without Making a Mess
Do this with the machine switched off and the tub cool, not at the end of a hot cycle. Then:
- Slide the lower basket out and unscrew the cap.
- On a first fill only, top the reservoir up with water first, as the settings chapter for your model describes. After that the reservoir already holds brine and only salt goes in.
- Pour the salt in with a funnel and stop when it is full. Some brine will overflow. That is expected.
- Screw the cap back down firmly and square, then wipe every grain of spilled salt out of the tub.
- Run a rinse or a short program straight away. Loose salt sitting on a stainless tub floor is worth clearing rather than leaving.
The Hardness Setting Is Half the Job
Filling the reservoir is only useful if the machine knows how hard your water is. Machines with the built-in softener carry a water-hardness setting in the settings menu, and the wording and the numbering vary between generations, so follow your own model's settings chapter. Get a real figure to enter rather than guessing: most water utilities publish an annual quality report, and a test strip gives you a reading for the tap the dishwasher is actually fed from. Set too low, you get scale and cloudy glass. Set far higher than necessary, you consume salt for no benefit.
In genuinely soft supply areas some models allow the softener to be turned down or off, and the manual for your model is the place that says so. If glassware has already gone permanently cloudy, that is etching rather than film and it does not wash off. Persistent scale on the element, a salt indicator that never goes out after a fill, or brine in the tub between cycles are worth a look, so book an Asko dishwasher repair rather than adding more salt.