Bill Redding:
I searched for the TDS-40 but cannot find it. They do show the TDS-4. Can you clarify? Thank you.

bronsht,

Oops! My mistake -- you're correct, it's "TDS-4" and not "40" -- I went back and corrected that post. Sorry I confused you (and other readers -- and I'd not know it was wrong unless someone told me so it'd STAY wrong forever -- thanks for telling me)...

IIRC, I got my HM TDS-4 here: http://www.amazon.com/HM-Digital-Thermo ... B0002T6L5M

[get some water hardness test-strips along with it and if your order is over $35 you get free shipping]

Also IIRC, this model adds "Automatic Temperature Compensation" that previous models didn't have (like the HM Digital TDS-3 meter).

Remember, when you get a numerical TDS result, you STILL don't know what % of that number is the pesky Calcium/Ca ion (or Magnesium/Mg, which is also responsible for scaling, although Ca is the major culprit), so you need to continue your "scientific water analysis" and do a more specific test, for hardness -- and Ca in particular.

But for sure, getting a TDS meter is the preferred starting point, so your FIRST "tool" should be a TDS meter, since to begin you need to get an actual numerical TDS value.

And although (as mentioned) that TDS number doesn't identify exactly WHAT "Solids" are in the water (could be organic matter, colloidal gold/silver (if so, you could become rich), uranium, lead, arsenic...who knows!) -- just how much "solids" there are as per ppm (Parts Per Million) -- it still reasonably can be concluded that the HIGHER the TDS number the HIGHER your water hardness is.

Use one of the TDS tables/charts to see where YOUR tap-water fits....like this one:

http://www.bracton.com/wp-content/uploa ... -chart.png

Good luck,

-- BR