How hard is the water in St. Tammany Parish, LA?

0.3 grains per gallon

You do not need a softener here.

The median hardness measured in St. Tammany Parish, LA is 5 mg/L as calcium carbonate, which is 0.3 gpg. That is soft on the USGS scale. It comes from 46 samples at 37 sites between 1990 and 2024, drawn from groundwater wells, which is what most taps and private wells in the county draw on.

How much it varies here

Half the sites came in between 0.2 and 0.6 gpg. The whole middle of that range gives the same answer, so a test of your own tap is unlikely to change it. Confidence in the county figure: high (how it is measured).

What to do next

You can skip the softener. At 0.3 gpg the most a softener would fix is the odd water spot. If a salesperson in St. Tammany Parish says otherwise, ask to see their reading in grains per gallon and compare it with this one.

More on when a softener is not worth it.

From 0.1 to 6.4 gpg

The softest single sample on record in St. Tammany Parish was 1.3 mg/L and the hardest 109 mg/L, an 84-fold gap. The top quarter of sites read above 0.6 gpg and the bottom quarter below 0.2 gpg.

Wells 0.3 gpg, rivers and lakes 3.2 gpg

46 groundwater samples from 37 wells put the median at 5.1 mg/L. 2,808 surface samples from 91 sites put it at 54 mg/L. In St. Tammany Parish the rivers and lakes come out 2.9 gpg harder. Here the surface water reads harder than the wells, which often points to streams fed by limestone springs or irrigation return flow. The two sources are close, so the county figure should hold whichever one your tap is on.

St. Tammany Parish against the rest of Louisiana

Among the 64 Louisiana counties with data, St. Tammany Parish is number 60 of 64 counting from the hardest. Across the whole country it is harder than 0% of counties.

Softest in Louisiana: Lincoln Parish at 0.1 gpg. Hardest: St. Bernard Parish at 53.9 gpg. Closest to St. Tammany Parish: Sabine Parish (0.3), West Baton Rouge Parish (0.3), Washington Parish (0.2).