Comment by mortos
19 days ago
TDS is just Total Dissolved Solids. What solids though you don't know and you could be adding carbon while removing others which is likely the case.
Also those dinky little TDS meters don't even measure TDS. They measure electrical conductivity and with a little math they use the EC as a proxy for TDS. It's typically only calibrated to one specific ion, others will be off by some factor. Also keep in mind TDS is expressed in PPM as CaCO3.
Yes, but be that as it may, at least it shows whether _any_ filtering is occurring at all. Which in the case of even a somewhat spent carbon filter is not a thing. RO does the job so well, you have to remineralize afterwards or the water doesn't taste like anything. You could literally pee into a jar and get fresh water on the other end. That's sort of what happens on sailing vessels that are equipped with water makers - they simply run sea water through RO.