The TDS (total dissolved solids, not salts) is a measurement of the water's ability to conduct electrical current. It is a very valid test and nothing about it is a scam.
The things dissolved in water allow it to conduct electrical current, remove them and the water conducts less current, it is measured with a TDS meter that converts the reading to ppm of TDS.
ROs produce high quality drinking and cooking water. Comparable and usually better quality than distilled water without the inefficiency and much higher expense. It is not a scam and the reject water should not be considered wasted anymore than the water you use to shower with, wash a vehicle or veggies or grow grass etc. etc. etc..
RO water is not acidic, it is aggressive to metals due to the DO and CO2 content. You test an RO's operation buy using a TDS meter to see the reduction of TDS between the raw water and the RO's product water. It usually is 90+ reduction when the membrane is new and the percentage spread slowly decreases as the membrane ages and when the TDS reaches a set point, you know to replace the membrane. No scam there. IIRC, RO was invented for the space shuttle.
The unethical, scam if you will but shouldn't, is the precipitation demo. And she may not know that because of her training; or lack thereof.
Gary Slusser
22 yrs in water treatment and well pumps, 13 yrs helping people on the 'net to help themselves.
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