According to Wikipedia, total dissolved solids (TDS) is defined as “the combined content of all inorganic and organic substances contained in a liquid that are present in a molecular, ionized or microgranular suspended form.” The article goes on to state that “total dissolved solids are differentiated from total suspended solids (TSS) in that the latter cannot pass through a sieve of two micrometers but are indefinitely suspended in solution.”
In other words, TDS is anything— other than the pure H2O—in water that you cannot see. This could include any salt, metal or mineral, and the lower the TDS level is, the purer the water.
So then why should TDS be measured? As an overall indicator of water purity, TDS is an especially important parameter, and more often than not, it is the first one tested. A TDS test is quick, easy and inexpensive. A single TDS meter can be used thousands of times, requiring nothing more than the occasional recalibration and new batteries.
Water filtration, treatment and purification often become a question of costeffectiveness. Knowing the TDS level will help determine what, if any, type of system or process is required. Along these lines, a TDS meter is an excellent tool for determining the efficacy of many types of water filtration and purification systems.
Many people still rely on the oldfashioned methods of time or flow to determine when the filter cartridge or membrane needs to be changed. Because usage may vary and the TDS levels of water supplies fluctuate, time and flow are far from precise methods. With improved technology in TDS measurement being coupled with accessible prices, the focus is definitely moving away from a reliance on time and flow.