Boston Water Is Soft. So That Film on Your Glasses Isn't Limescale

MWRA water sits comfortably in the first band. That is not a marketing claim, it is in the report. Look yours up before you spend money on a water softener a plumber quoted you for a dishwasher problem.

So what is the film?

Two different things, and they feel different under your finger.

• Chalky, wipes off dry, worse on plastic than glass — undissolved detergent. There is not enough mineral in the water to consume it, so the surplus precipitates back onto the load during the dry cycle.
• Cloudy, will not wipe off, glass looks etched even when dry — this is permanent. It is silica leaching out of the glass itself, and soft water plus high temperature plus aggressive detergent accelerates it. Once a glass is etched, no repair or product brings it back.

The second one is the reason this matters. People respond to film by adding more detergent and running hotter, which is exactly the combination that etches glassware permanently. I have replaced a lot of perfectly healthy circulation pumps for customers who were convinced the machine was broken, and the machine was fine.

The fix, in order

1. Cut the detergent, hard. Most people fill the main cup. In MWRA water, a third of a standard pod's worth, or roughly a teaspoon of powder, cleans a normal load. If you use pods and cannot dose them down, switch to powder or gel so you can.
2. Do not skip rinse aid. Counter-intuitive, but rinse aid is a surfactant, not a descaler — it breaks water tension so the load sheets dry instead of spotting. Soft water needs it as much as hard.
3. Turn the salt reservoir off if your machine has one. Bosch, Miele, Asko and Blomberg machines sold in Europe and often carried over here have a built-in water softener with a salt compartment. Running it on MWRA water over-softens water that was already soft and makes etching worse. Set the hardness setting to its lowest value; the manual will tell you where.
4. Check the water temperature at the tap, not the machine. Run the kitchen hot tap until it is hot, then start the cycle. A dishwasher that has to heat its own fill from cold extends the cycle and leaves detergent sitting undissolved at the start.

When it genuinely is the machine

Do all of the above for two weeks. If the film persists, now it is worth a service call, and the usual culprits are:

• A blocked lower wash arm — the end holes silt up with label paper and seeds. The upper rack cleans and the lower does not.
• A failed heating element or thermistor — the cycle never reaches temperature, so the detergent never fully dissolves. This shows up as film plus wet dishes at the end.
• A worn or gummed-up detergent dispenser flap that opens early, dumping the whole dose into the pre-wash where it gets pumped away, or late, dumping it into the rinse.

Those are all fixable and none of them are expensive relative to a new machine.

The one Boston exception

Not everyone in our service area is on MWRA. A good part of Essex County — Beverly, Danvers, Salem, Gloucester, Rockport, Ipswich, Boxford, Middleton, Hamilton and Wenham among them — draws on local reservoirs and wells, and hardness varies a lot from town to town and even between sources within one town. If you are north of Lynn, do not assume you have soft water. Pull the town's report, or the well test if you are on a private well, and read the actual number. Everything in this article inverts if that number is over 120.

We cover both sides of that line, which is why our first question on a "my dishwasher leaves film" call is which town you are in.