Need help determining my water quality.

This might be a stupid question so bear with me please. My city has online a pretty thorough quality report with ppm of lots of different inorganics. The problem is that it lists the wells servicing my address and their relative usage. In some areas the ppm differ pretty widely. Is there any way to approximate a water profile using a weighted average or something? Or is this inherently going to be too inexact to be of much use?

The website looks something like this (hard to get formatting right):


Winter Well Usage

Well Percent
Number Usage Quality Report


24 40-60 24 (PDF)
30 20-40 30 (PDF)
18 05-10 18 (PDF)
14 05-10 14 (PDF)

I don't know what any of those numbers mean so I can't be of much help other than to say if the dispersion is narrow i.e. if one well isn't much different from another and if an individual well's mineral contents doesn't change much over time then an average would be a good approximation.

Sorry I did my best to represent the graph on the site but it's not really clear...I think HBT turns my attempts at tabbing via space bar into single spaces. It's basically stating that 40-60 percent of the water comes from Well 24, 20-40 percent comes from Well 30, etc. I would assume that a given well doesn't change much over time, but the dispersion varies a good bit from one mineral to the other.

If, for example, well 24 ran 2 mg/L Ca++ and well 30 ran 100 then an average (50*2 + 30*100)/80 would probably not be a very good representation of any particular sample (though you could get lucky). OTOH if well 24 ran 80 and well 30 100 then an average probably would be a good guess. If you knew the mean and standard deviation for each mineral for each well you could Monte Carlo up something which would give you an idea of mean and standard deviation. Doesn't sound promising. Could it be that the supplier blends wells in order to try to meet some standard profile? If so, find out what that is and you should be OK.