How can you decrease tds in product water to RO?

reverse osmosis consists on adding a semi-permeable membrane and adding pressure to the water source side forcing the water to flow into the less concentrating tank (the processed water). The contaminant molecules will not be able to pass through the membrane. If the water contains chlorine which damages the RO membrane we need to a add a carbon filter in order to save it. TDS will decrease up to 90% with this procedure but we need to make sure to clean the source side tank periodically in order to keep it from become so concentrated that if forms a scale on the membrane. 

TDS level down so use Reverse osmosis Procedure apply.

 The RO is designed to minimize total dissolved solids (TDS) from the feed stream. Dissolved solids can come from a variety of sources and are present in virtually all water supplies.  The amount of TDS present determines whether or not you can provide a spot free solution in your wash. The industry standard for spot free rinse water is less than 40 ppm (parts per million) TDS. The product water after the RO system is predicated on the amount of TDS in the feed water to be treated. Most RO membranes can remove on average 98% of the dissolved solids in the water.  Typical feed water from most city water supplies are less than 500 ppm therefore the expected results after the RO system is approximately 10 ppm.

All RO systems eventually will require cleaning.  Cleaning is recommended when your RO shows evidence of fouling. The time to clean your membranes are either just prior to a long term shutdown, or as a matter deterioration of performance.  Fouling characteristics that signal you need to clean are a  10-15% decrease in permeate flow, a 10-15% decrease in permeate quality, or a 10-15% increase in pressure drop as measured between the feed and concentrate flow.

first of all, we  should know that TDS comes from Some dissolved solids come from organic sources such as leaves, silt, plankton, and industrial waste and sewage. Other sources come from runoff from urban areas, road salts used on street during the winter, and fertilizers and pesticides used on lawns and farms.

2. Dissolved solids also come from inorganic materials such as rocks and air that may contain calcium bicarbonate, nitrogen, iron phosphorous, sulfur, and other minerals. Many of these materials form salts, which are compounds that contain both a metal and a nonmetal. Salts usually dissolve in water forming ions. Ions are particles that have a positive or negative charge.

3. Water may also pick up metals such as lead or copper as they travel through pipes used to distribute water to consumers.

So, to get good water quality before using RO we should use some 1. Carbon Filters or  make Distillation  to the water  (total reduction - flat taste)

or make  DI Deionization  (usually a final polishing filter following a RO Reverse Osmosis filtration system to eliminate TDS)