One of the most common complaints raised by consumers using automatic dishwashers are spots and streaks on dishes, glassware, and silverware, or a cloudy or milk like film on glassware. These complaints can be broken down into three areas of conditions: 1.) Hard water causing calcium spotting. 2.) Soft water causing sodium spotting or etching, or 3.) Silica spotting due to high silica content in the water supply. The following information and quick tests, will help the water professional to tell the difference. He can then recommend corrective action on each and solve those nagging complaints.
Hard water spotting/filming: Spots left by hard water (calcium and magnesium deposits) usually require harsh abrasives or an acid cleaner to remove them. A quick check for this condition would be soaking the glass(s) in a vinegar or lemon juice solution and if the spots/film dissolves-it's caused by hard water. A properly sized water softener will solve this problem.
Soft water spotting or etching: So now they have a water softener and they still have spots or a milky film on the glassware or dishes. Softened water contains sodium salts, which can leave spots on glassware. These can be easily wiped off with a damp cloth or rinsed off with a little fresh water. Using an additional wetting agent may help eliminate the spots and/or let the dishes air dry (skip the drying cycle).
Soft water etching (or filming) can be caused by detergents containing phosphates or other sequestering agents used to tie up the waters hardness. Softened water allows these agents to attack the glassware resulting in white streaks or film, which cannot be removed-the glass is eaten away. An early warning signal of serious etching is the appearance of a rainbow-colored film on the glassware. Using a low-phosphate detergent formulated for use in soft water will minimize the problem. Also, cutting back on the amount of detergent used, using a cycle that has a longer rinse time, keeping the water heater temperature less than 140 degrees and/or allowing the dishes to air dry will help reduce this problem.
Silica Spotting: This is generally a rare condition and is not removed by a water softener. You can not smell or taste silica nor does it leave a stain, but it will leave a white film on glassware that cannot be removed. A quick way to tell the difference between a hard water film and silica is to soak the glasses in a vinegar or lemon juice solution. If the film dissolves, your back to a hard water problem. If it doesn't dissolve and can be scratched off with a razor blade or pin point, it's a silica film. There is no practical way to remove silica from a residential water supply or the film caused by it. All dishwasher manufacturers state in their manuals that delicate china and glassware should always be hand washed and towel dried.