Hardness Discrepancy?

So a while back I got a report from the water treatment plant that supplies my water, and according to them the "Total Hardness" is 100ppm.

Today i had somebody here to check out my water softener, and he tested my water (pre-softener) and he said it tested at 13-14 grains per gallon hardness level. I put this into a online conversion to ppm, and that converts to 222-239ppm hardness.

I know this guys test wasn't super accurate (he was using a kit where he had to count the number of drops it took to turn his sample to a different color), but that seem to be a very significant difference.

Is there any possible explanation to this?

There are a couple. First and most obvious is the one you mentioned: drop count tests aren't very accurate. The problem could be in the strength of the acid, the measurement of the test volume, the color and intensity of the light in which the measurement was taken or the guy could even be color blind. The other possibility has to do with the way utilities take and process measurements. The number you got from the utility could be a grab sample or it could be a weekly, monthly or annual average. The parameters of waters from some utilities vary appreciably seasonally especially where a utility draws from several sources, relies on nearby utilities for additional supply in time of high demand, etc.

My guess is that 100ppm is way closer to the truth than 200+. Your filter guy could be feathering his nest. It’s probably the same kit they use to scare people into buying water treatment.

My water dept says 100-125ppm. I asked the chemist if that was a seasonal variation, and she said no, it depends on the treatment. I thought that was weird, as if the treatment was fairly random.

I guess the moral of the story is to not get too complacent about the numbers on the water report. It’s a moving target, or maybe even a total crap-shoot. Keep an open mind and use a pH meter.

Water utilities 'tune' for a 'corrosivity' index of which there are several and many of which involve saturation pH i.e. the pH at which calcium carbonate will start to precipitate as compared to the pH of the water given the rest of the chemistry. Thus they may well be adjusting the dosing of a calcium salt to meet their corrosivity requirement. The point is that there are lots of reasons why a suppliers water may vary in hardness, alkalinity, chloride content etc. Some suppliers, OTOH, are steady as a rock year round. The best situation occurs if you are lucky enough to have a supplier that gives a detailed breakdown month by month. Otherwise your best bet is to obtain kits and measure yourself with multiple sample to Ward Labs being second best.

What sort of a kit? Would an aquarium kit be adequate?

I use sodium carbonate to treat my bath water, and it seems like I need to add more in hot weather, less a few days after a big rain. Go figure that it would be more complicated than that.

Thanks AJ, you’re a good teacher.

Is the softener the only treatment system you have? Some pH adjustment systems will raise the hardness and that could account for some of the change.

Wynne-R said:

What sort of a kit? Would an aquarium kit with be adequate?

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Should be. The next step up is hundreds of dollars.

MDVDuber said:

Is the softener the only treatment system you have? Some pH adjustment systems will raise the hardness and that could account for some of the change.

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That's a good question, I don't think there is anything else, but I'm not sure. It is all rainsoft brand, they service out softener and RO system on our kitchen sink, I rent so I didn't have the system installed and don't know all of the details. I'll probably give the treatment plant a call again for more info and see if I can get some historical monthly data to see if it varies, and ask them what they think of this 200+ measurement.