This is the appliance complaint most often solved by doing less rather than buying something, and the reason is specific to the water here.
The regional fact most advice gets wrong
Greater Boston drinks MWRA water from the Quabbin and Wachusett reservoirs; Cambridge draws its own supply from Fresh Pond. Both are naturally soft — roughly one to two grains per gallon — and both are dosed with sodium carbonate to raise pH, which protects the old lead and copper service lines in this housing stock rather than doing anything to your dishes.
Nearly all appliance advice written for a national audience assumes moderately hard water, because most of the country has it. So the standard answer to cloudy glassware — descale, use more detergent, add a rinse booster for hard water — is not only unhelpful here, it usually makes the problem worse.
Telling the two apart in thirty seconds
The test costs nothing.
Take a cloudy glass and soak it in white vinegar for about five minutes.
- •The film dissolves and the glass is clear. That is mineral deposit — genuine hard-water scale. Real, but uncommon inside the MWRA footprint.
- •The film stays. That is detergent residue, or etching. Detergent residue wipes off with a cloth after soaking; etching does not come off at all, because it is permanent damage to the glass surface.
Inside Boston, Cambridge, Somerville, Brookline, Newton and the inner ring, the answer is overwhelmingly the second one.
Why soft water plus normal detergent equals film
Detergent is formulated with builders that bind the calcium and magnesium in hard water so the surfactants can work. In soft water there is very little for those builders to bind to, so the excess stays in solution, does not rinse away cleanly, and deposits on everything as the load dries.
The result looks exactly like scale to the naked eye and is the opposite problem.
Worse, in very soft water an aggressive detergent can etch glassware — a permanent cloudiness caused by the alkalinity leaching material out of the glass surface. Once glasses are etched they cannot be recovered. If your glasses have gradually gone cloudy over a year or two and vinegar does nothing, that is what happened, and the fix is to stop it happening to the next set.
What actually works here
Halve the detergent. Start there. If you use tablets, break them in half or use the smaller-dose product. Most households in this city are running two to three times what the load needs.
Use rinse aid, and keep it topped up. It reduces surface tension so water sheets off rather than beading and drying in place. It matters more in soft water, not less, and it matters enormously on Bosch and other condensation-drying machines.
Set the machine's water hardness to its lowest setting if it has one. Many European-built machines — Bosch, Miele, Siemens — have a built-in softener with a hardness setting, and one set for hard water in soft water will over-regenerate and add salt to the problem.
Skip the pre-rinse. Modern dishwashers with a soil sensor dose based on how dirty the load is. Rinse everything first and the machine reads a clean load, doses light, and you get poor results — or reads it normally and now has far more detergent than soil to work on. Scrape, do not rinse.
Do not add a hard-water booster. In this water it is the wrong direction.
Give it two or three cycles. The change is usually obvious.
Where in our footprint this advice flips
Not everywhere we work is on the MWRA system, and in those places the standard hard-water guidance is correct.
The well-supplied towns at the edge of the footprint — Dedham, Needham, Wellesley, Dover, Canton, Westwood, and the northern towns of Woburn, Burlington and North Reading — draw on local wells and are genuinely harder. So does essentially all of Essex County: Lynn, Salem, Beverly, Peabody, Danvers, Gloucester and Rockport run their own surface systems, and the inland North Shore towns are on private wells.
In those places scale is a real finding. Descale on a routine rather than in response to a symptom, keep the machine's hardness setting matched to the supply, and expect heating elements, spray jets and ice makers to accumulate deposit over time.
If you are unsure which side of that line you are on, your town's water department publishes an annual quality report with the hardness in it.
The film that is neither
Two other things get reported as cloudy glassware.
Grit and sediment on the dishes. Not water chemistry at all. The MWRA supply is soft but the pipes carrying it frequently are not new, and century-old iron mains and building risers shed fine particulate — especially after street work, a hydrant flush or a service-line replacement. It lands in the inlet screen and the dishwasher's own filter. Clean both.
Food redeposited across the load. That is the filter, not the water. Bosch and most modern quiet machines have no food grinder, which is precisely why they are quiet, so anything solid stays in the filter at the bottom of the tub until someone takes it out. Monthly. Twist out the cylinder, lift the mesh, rinse it under the tap.
When it is genuinely the machine
If the dosing is right, the rinse aid is full, the filter is clean, and the results are still poor, then look at the appliance:
- •Spray arms with blocked jets, or not turning freely. Take them off and check every hole.
- •Water temperature. These machines want an incoming supply around 120°F. In a triple-decker where the laundry sink, three units and the dishwasher share one tank, the dishwasher may simply not be getting hot water. Run the nearest tap hot before starting the machine and see whether results change.
- •The heating element or flow-through heater, which is what actually gets the wash water to temperature.
- •The circulation pump, if the spray pressure is visibly weak.
Those are real repairs. But we would rather you tried the free fix first, because in this city it works more often than not.