Just tested NYC water coming out of our pipes (Bklyn to be specific) with a Digital TDS Meter and the reading I got was 21 PPM
After I Purified it I got a clean reading of 1 PPM
Anyone else getting similar , worse or better before and after?
Guys, just for sake of clarity, the TDS tells you nothing about how clean, dirty, or whatever the water is, it just tells you whether there are dissolved ions in the water or now. A TDS of 1000 is harmless if it's table salt (NaCl) giving the reading, whereas a TDS of 1-2 could well be quite deadly it's cyanide (CN-) giving you that reading.
In general, we assume that there are nasty things in tap water we don't want in our tanks (usually true). If we remove most of those nasty things so that we get a TDS less than 1, we can be reasonably confident our water is ok to use without problems. However, if there is nothing particularly troublesome in the water, the TDS is irrelevant, whereas if there is some very noxious compound, even a TDS of 1 may not be good enough.
Years ago I had a tank at my parent's house. Their tap water is from a well, out in the country in MI. The TDS was well over 400 due to dissolved limestone (CaCO3) in the water. Several times when I was out of RO I used just tap water to top off that tank, keeping my fingers crossed. The tank thrived. In fact, I eventually realized that there were no negatives from using this water (it seemd to be very clean, had undetectable nutrients, etc.) and ended up using straight tap water for that tank for a couple of years with very good results. If I were doing this in most municipalities, the tank would have been a disgusting mess of algae and death if only for the very high phoshate levels.
Anyway, just to reiterate, the TDS tells you nothing about how clean or dirty water is, it just tells you how much charged 'stuff' is in the water. Pure sea water at a salinity of 35 ppt will give you a TDS of about 35,000 because it has a heck of a lot of dissolved ions.