I didn't see St3ve asking me if I knew that silty spring runoff was gong to raise TDS in municipal sources or if it was just a guess. Sorry it took so long for a response:
Guys, this isn't magic; it's advanced common sense. Once you've fallen out of a tree, you should know that jumping off a cliff will hurt too- so there's no need to go repeating the experiment, right?
Rivers rise in the spring, swollen with melted snow, and they scour the riverbeds and pick up a load of dissolved solids along with sand, silt and even rocks. Same thing on flatland, only now it's rainwater leaching various salts from the land, plus agricultural runoff from chemical fertilizers and the like. This seasonal flush then diminishes as the water levels fall over the late summer and on through winter, leading to lower TDS.
This is also true on a short term basis; it's not news to anyone with a sump pump in their basement that wet weather can affect groundwater, often with a very short delay. Again, it stands to simple reasoning that as this groundwater level fluctuates, water is moving and as it moves it picks up and dissolves more solids. This time, the relationship is usually backwards; rising groundwater generally has a lower TDS reading than falling. In other words, drought tends to concentrates minerals in groundwater.
I am fortunate to live in a health conscious community (ok, so they're a little nutty about it, really!) that asks its water department to regularly post their water quality findings on their website, along with explanations of how and why dissolved solids get in there and when to expect them. I read up, and that's how I was able to confirm my earlier suspicions about seasonal TDS variances.
My point here is to educate yourself- the more you know, the more you can recognize and deal with effectively.
One more clarification to handle: chlorine vs. chloride vs. chloramine. Squiggly here would be able to give you the in depth deets, but the bottom line is that chlorine and chlorides in solution act very similar and will evaporate by themselves. Chloramines will NOT, and so you need to either filter it out or add something to the water to help it outgas. One is bleach, in very small amounts; maybe 1ml/gallon, then let it sit and outgas- or aerate it- for 24-48 hours. Another method is sugar. Yes, Ms. Poppins, a tiny bit of sugar (1-2 ml/gallon) will also encourage the conversion of chloramines into a form that will outgas.
In these low concentrations, the chlorine and/or chloramines will not affect you or your plants- but they will very likely screw with any microbial life you put in there, as that's the original intention of adding it in the first place; to kill off any nasty bugs in the water that might make people sick. Because I currently run sterile RDWC, I use tapwater without a second thought; when I start playing with microbial teas, I will have to be more careful.
