Can water chemistry change?

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Well-Known Member
Feb 14, 2011
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I'm about to send a sample of my well water off to Ward Labs, and got to thinking - does well water chemistry change significantly over the seasons?
Depends on whether or not your utility switches water sources or not.
Oops, I don't think he read "well water". I think public water systems are much more susceptible to shifting conditions across seasons because they switch sources. It wouldn't hurt to have it tested with a 6 month offset just to be sure. It's cheap enough.
It makes sense that it would change some with the seasons... I would bet it would be a little harder in the winter. It would be fun to see.
OK. I will set a reminder to do another test in six months, just out of curiosity. Will post back here then.

Thanks, guys.
Yes, well water varies somewhat depending on what's happening to the aquifer that feeds the well. But the variations shouldn't be great. In my own experience [EDIT] with a deep (270 ft) well [/EDIT] alkalinity varies between 70 and 80 and total hardness hangs in pretty close to 110 based on essentially random sampling (by which I mean that I do not measure water parameters daily, weekly or even monthly but only every so often just to see that things aren't changing).
My well isn't very deep and it is very dependent on the amount of rainfall the prior 3 months. It gets harder during the summer as the underground flow rate slows. I use it to water the plants.

Fortunately, I'm also hooked up to a community system that has deep wells. The water is consistently great.
Here are my 2 water reports from roughly 13 months apart. They do vary a little bit.

pH 7.7
Total Dissolved Solids (TDS) Est 447
Electrical Conductivity, mmho/cm 0.75
Cations / Anions, me/L / 7.6 / 8.3
Sodium, Na 13
Potassium, K 1
Calcium, Ca 78
Magnesium, Mg 46
Total Hardness, CaCO3 387
Nitrate, NO3-N 4.8 (SAFE)
Sulfate, SO4-S 6
Chloride, Cl 36
Carbonate, CO3 < 1
Bicarbonate, HCO3 358
Total Alkalinity, CaCO3 293
Fluoride, F 1.31
Total Iron, Fe < 0.01

pH 7.5
Total Dissolved Solids (TDS) Est 443
Electrical Conductivity, mmho/cm 0.74
Cations / Anions, me/L / 8.3 / 8.4
Sodium, Na 17
Potassium, K < 1
Calcium, Ca 81
Magnesium, Mg 44
Total Hardness, CaCO3 386
Nitrate, NO3-N 5.0 (SAFE
Sulfate, SO4-S 6
Chloride, Cl 42
Carbonate, CO3 < 1
Bicarbonate, HCO3 391
Total Alkalinity, CaCO 320
That's not much and some of it is in measurement error. Note that the imbalance is 0.7 mEq/L in the first report and only 0.1 in the second. For reference, 1 mEq/L would represents 50 ppm as CaCO3 if all attributable to hardness or all to alkalinity.
I think OP was speculating about seasonal changes, and 13 months apart is pretty much the same season
Correct, I was wondering about it based on the time of year. But year to year at about the same time is also interesting.
If the groundwater source is interconnected with a local surface water, then it could be possible to see some change in water quality due to relative levels in the water sources and consumption from your well and other nearby wells.

In the case of Burton on Trent, the upwelling of sulfate-laden groundwater from a deeper aquifer into the surficial Sand and Gravel aquifer gives that area its unique water character. The Trent River sits on the Sand and Gravel aquifer and generally drains water from that surficial aquifer. But when a brewery and other industries extract a lot of water from the Sand and Gravel aquifer, the net flow can be from the river into the aquifer. That ends up diluting the sulfate concentrations in the groundwater with the less mineralized river water. The deep aquifer can only deliver so much water since it is not very permeable, but the Sand and Gravel aquifer can many magnitudes more water.

The same thing can happen to any well owner that is near a lake or river and their well taps into the local surficial aquifer.
I know that at my folks house, after a heavy rain and before they put in over flow tanks and the house filter, the water was reddish from the clay we have out here. It makes sense that even after the clay has settled, that there might be some kind of elevated level of minerals in the water. It would be really interesting to see
I'm going to try to help to find out! Haven't gotten my first sample back from Ward Labs yet.

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