JimScott's question about RO units got me thinking about my water.
Our tap water comes in at around 200ppm, so I use either collected rain water, or buy RO water at the local Kroger store. That usually measures around 4ppm if I catch the RO unit after a recent servicing.
I use a cheapo TDS meter bought from Amazon several years ago. Should I worry about it drifting out of calibration?
My current readings agree pretty well with past readings from various sources, so I'm not worried about the current calibration, I was just curious about how well these things generally hold calibration over several years.