"A test for TDS does not measure chemicals or pathogens; a low TDS count does not mean that water is safe to drink."
http://www.purewatergazette.net/blog/total-dissolved-solids-june-15-2014/
Ya your EC or TDS of 0 means nothing in terms of pathogens or viruses or heavy metals or anything. Turbididity is a measure of the suspended solids in the liquid, and EC is a measure of the electrical conductivity of the solution. So you could still have plenty of stuff in your water with a 0ppm or 0 TDS reading.
Not sure why the one dude thinks he knows more about your situation than you do, but I think you're on to something. If the change of water helped, then keep it up. Seems easy enough. Good luck.