I installed iSpring rcc7 Reverse Osmosis filter 3 months ago.

I bought HM Digital TDS-EZ Tester from Amazon, and found the TDS (Total Dissolved Solids) in unit of PPM (Part Per Million) is 496 PPM in our tap water. I got scared, and installed Reverse Osmosis filter in one week. 

After I installed the filter, TDS becomes 15-18 PPM. 

I tested bottle water, TDS is 16 PPM. The water came out of my refrigerator filter is 485 PPM, this filter is useless. The same for pitcher water filter.