Having bought a TDS meter off-the-shelf from a store, I came across this notice: http://www.reagecon.com/PerspectiveCMS/uploads/TDS_Tech_Tip.pdf Now though I am going to use the TDS meter for water testing purposes(ground water hardness,hence potability,subsequently use the measurements towards design of custom Reverse Osmosis systems,presently for domestic markets only), How should I calibrate the TDS meter.I sometimes get to collect sediments of hardwater that deposits by themselves in overhead plastic tanks which are directly exposed to tropical heat (upto 35degree centigrade), in 6month intervals. (1)I would like to know How do I CALIBRATE the TDS meter for it to provide accurate measurements in the aforesaid context. (2) Whether there are any general DESIGN Guides to RO Systems (D-I-Y types) based on a conceptual+empirical framework from components available in market.Some resources reference will be appreciated. (3) How to "RETREAT" the Output water of such RO assemblies so that it can be freely used to water plants of small domestic gardens or even a couple of trees, like Coconut trees,flowering plants,etc. What is the Soil characteristic threshold that is considered normal?