Tap water ppm reading

chris669 · Jul 21, 2015

Hi
Just got my tds meter and have been testing water
My tap water is 300ppm ,tested bottled water at 165ppm and distilled water at 0.01
Waiting for my ro unit but interested to know if this is high or the norm

redfishbluefish · Jul 21, 2015

Where do you live and is it well or city water? I would say 300 is in the "meat" of the bell curve, maybe slightly towards the high side. A high quality membrane will have no problem knocking that down to 5-6 tds and the DI resin with knock it down to zero.

The bottled water doesn't surprise me. I had a friend who was a QC chemist at a milk company and he tested a bunch of bottled waters. You wouldn't believe how "dirty" most bottled waters are......including bacteria.

Also, unless you have an extremely expensive TDS meter, I don't believe you're reading to the hundredth position.....no decimal point....just 1 TDS.

Randy Holmes-Farley · Jul 21, 2015

FWIW, even the best conductivity meters, costing $1,000-$10,000 do not usually read ppm TDS to less than 0.1 ppm TDS. When scientists are interested in those low levels they use different units. Absolutely pure water should read about 0.055 uS/cm, or the equivalent of 0.02 to 0.03 ppm TDS due to the presence of H+ and OH- naturally in water which provide conductivity.

AZDesertRat · Jul 21, 2015

The average TDS nationwide is around 250. Your meter does not actually have a decimal point, the dot is a power ON indicator so the distilled water reading is actually 1 TDS not 0.01 . Even more expensive meters such as the HM Digital COM-100 only read to one decimal point as in 0.1.

TDS is a mathematical calculation using conductivity and temperature and not nearly as accurate as actual conductivity or resistivity but fine for our hobbyist uses.