Expert: Profile Closed - 1/12/2010

Question
We have recently moved to an area that has hard water--not hard enough to necessitate a water-softening system, but hard enough to form a milky film on glassware washed in our dishwasher.  Products such as "Finish" (fort use with automatic dishwasher detergent) are quite expensive.  I have tried Calgon powder water softener in a box, which is also expensive.  Are there any chemicals one can purchase that would be the equivalent? "Calgon" does not list any ingredients and says only "contains no phosphorus"; "Finish" contains "not more than 21% phosphorus" and also contains sodium metasilicate, sodium tripolyphosphate and active organic chlorine; however, I am unable to find a local source for these, nor what quantities of each might be needed.  If you are able to offer any suggestions, I would be greatly appreciative.  Thank you for your willingness to help!

Answer
Hello there, and thank you for your question.

I'm sorry to hear you're having problems; our water here is quite hard and we have similar trouble with washing glassware.

Calgon and similar products all work by capturing the metal ions responsible for making water hard (e.g. calcium) in a "complex", where the metal is caught up in the structure of a larger molecule. Calgon uses sodium-based compounds to achieve this, but it would be difficult to access the compounds on a small-scale, and would be expensive.

A good method for generally softening water not used for human or animal consumption (e.g. in washing machines) is to add four tablespoons each of borax and washing soda to a gallon of water, and add a cupful of this to the water before it's used (e.g. putting a cupful in with the washing).

However, the problem with the dishwasher is that the water is sprayed directly from the mains on to the cups etc; there's no way of making sure the solution mixes in well with the water (unlike in the washing machine, where it mixes in with the wash water as the clothes are spun). So this probably won't be of much use given that your problem centers on the dishwasher.

In the short-term, I would suggest using a lower-than-recommended amount of detergent in the machine, because the film you notice is produced when the detergent interacts with the hard water - lower the amount of detergent and you lower the chance of forming a film. Detergent portion-sizes are always over-estimated on packets (partly to ensure that there is always enough detergent regardless of the size of the machine, and partly because it encourages consumers to use up the detergent faster and so to have to buy more!). We use half the recommended dosage, and get fantastic results and much reduced film formation, but you may have to experiment to get the right dosage for your machine.

Short of that, because of the dishwasher's need to use mains water directly, your only option would be a small water softener on the incoming water line. The initial investment for such a unit is not overly large, and only common salt is required every so often to refresh them. If lowering the amount of detergent is not sufficient to stop the problem, I think that's likely to be your only option.

Apologies for not being able to be of more help; if you have any further questions or points you want to discuss about this problem, I'm more than happy to accept follow-ups.

Wishing you a happy 2010, best wishes,
George