[Killietalk] TDS vs Conductivity

[Ron Schulz <ron_schulz at gmail.com>]

What is the relationship between conductivity and TDS?. I have a Hach
conductivity meter which consistently measures my well water at 270uS/cm.
The hardness of my water is consistently around 130ppm as CaCO3  measured
with a Lamotte test kit. When I measure the conductivity of rain water off
my roof, I get around 35-40uS/cm. The hardness of the rain water measures 0.
Are these measurements  consistent with the assumption that  the
overwhelming cation species is Ca++ with little  other contributing species?
.......................Ron Schulz....... Dutchess County NY
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