Update: September 2013 – A Mystery Solved!
Why was our TDS typically only about 26 PPM when we have an RO system with a re-mineralization filter? Especially, when our water & tea taste so good!
Recently, I was reflecting on the following:
“Water with 50 – 150 ppm total dissolved solids (TDS) or 1 to 3 grains hardness provides the best results, according to the Tea Association of the USA.” http://www.teaandcoffee.net/0609/tea.htm
A water softener is required for our very hard, 450’-deep, well water. In addition, we need an RO system due to the very high level of TDS and to remove the sodium added by the water softener.
An RO system removes all the impurities and excessive dissolved solids and with it all the beneficial minerals that enhance the flavor of water. This is why we made sure to purchase an RO system that has a re-mineralization filter, a filter that adds back the beneficial minerals.
So why, why was our TDS typically only about 26 PPM when we have an RO system with a re-mineralization filter? This situation did not make sense! Both our water and tea taste great! So why wasn’t our TDS higher? I had to investigate!
When we purchased our RO system, we also ordered a TDS meter to monitor the performance of it. (http://steepster.com/teas/teaware/39474-hm-digital-dm-1-in-line-dual-tds-monitor) This meter displays the TDS both before and after the RO system. The kind folks at Abundant Flow Water installed the TDS meter for us so there was no “assembly required” (unlike children’s Christmas presents) before I installed it. Since I had not personally installed the TDS monitor, I naturally wasn’t specifically aware of where the “TDS out” sensor had been installed.
Fortunately, I installed the RO system in the basement rather than in the under-sink kitchen cabinet where it’s cramped and dark. I turned on the twin-40W florescent tube shop light in the basement, which is directly above the laundry tub & RO system and then began following water flow path through the RO.
The “TDS In” sensor was after all the pre-filters and just before the RO membrane – right where it should be located. The “TDS Out” sensor was just after the RO membrane. From an RO maintenance perspective, that made sense. TDS measurements immediately before and after the membrane are what’s used to calculate “% rejection” – the parameter that determines when to replace the RO membrane (about every 3 years).
So what about the TDS of the water we actually drink? Since the “TDS Out” sensor is immediately after the RO membrane, it is before the re-mineralization filter! In other words, the “TDS Out” reading does not include the contribution of the re-mineralization filter.
Mystery solved! We have great tasting water & tea even though the TDS meter displays 26 PPM because the “TDS Out” doesn’t include the beneficial minerals added by the Aptera filter.
Thus, all my tasting notes to date, have under reported the actual TDS value of the water used for brewing tea. The water we enjoy every day has a higher TDS value.
Based on this discovery, I’ve now added an additional fitting to our RO System so the output sensor can be located either after the RO membrane for maintenance purposes, or after the Aptera filter to monitor the TDS of water we consume.