Free Nautical Charts - Why is water in coastal regions less hard than in the heartland of america?

Why is water in coastal regions less hard than in the heartland of america?

In theory, I would guess that this is related to precipitation originating from seawater, but because saltwater is so rich in minerals and salts, this seems absolutely counterintuitive, because seawater would likely be very hard. so what is the relation? Looking at the map of water hardness provided by USGS, there definitely seems to be a trend... help?

Public Comments

Estuarial water tends to come from rivers, while mid-continent water tends to come from wells. Well water is far more likely to contain dissolved salts than surface water.
Hardness in water is caused by compounds of calcium and magnesium. Since ALL water travels to a sea either above or below ground the hardness in the inland waters would be greatly diuted once it reaches the sea, Keep in mind the sea water will be very "brackish" due to the salt concentration..
Rainwater is soft. What causes hard water is the type of rock it moves through. Hard rock does not give anything up to the water and it remains soft. Limestone and the softer rocks give off minerals to the water which makes it hard. Therefore there is no relation between coastal and inland areas it is all to do with the rock structures. Incidentally if you live with hard water you are lucky - it has been shown that hard water significantly reduces the risk of heart disease, heart attacks and strokes!!!