There are many different components of water quality. While acidity, bacteria and hardness are among the better known, inside the trade one of the key components to water quality is something called Total Dissolved Solids (TDS). TDS is the measurement of the combined amount of organic and inorganic matter contained in water and it is measured in parts per million (ppm). The key here is that the matter is dissolved, which means that the matter has become part of the water. TDS is like putting salt into water, as you add the salt it disappears into the water. Pure water would have a TDS of 0ppm. Typical well systems have a TDS anywhere from 50 to 940ppm (our office’s personal record). On average, our customers well water TDS is 150-250ppm.
What makes up TDS in water is generally not known without a laboratory doing a very thorough test on a water sample. TDS can be anything from the chlorine/fluorine cities put into water to minerals dissolved into the water while it is underground to nitrates from fertilizer on wells that are near farms. It is really just a numeric amount of the overall “stuff” that has dissolved into your water. There are always exceptions to the rule, but generally you cannot conclude that a TDS of 500ppm is more of a concern than a TDS of 150ppm. It just depends on what has dissolved into the water to raise the TDS. But the TDS test does not tell us what has dissolved into the water, just how much. Figuring out if part of the TDS is harmful would need to be determined by a separate test, such as chlorine, bacteria, or hardness test. In the rare case your water is making you sick, a laboratory test would be needed. But those are all separate well water issues!
So why are we talking about TDS if it doesn’t indicate harmful substances in your water? Water can only dissolve so much matter before it becomes “full”. Once water becomes “full” any additional matter added to it will not dissolve and just become suspended in the water. Add a tablespoon of salt to a cup of water and it will dissolve. Keep adding salt, however, and eventually the water will not be able to handle any more and the salt will just pile up on the bottom of the glass. The same thing can happen with well water when trying to treat it. Systems such as sediment filters and UV lights remove the “bad components” from the water. But systems such as acid neutralizers and carbon filters dissolve “good components” into water in order to eliminate (or neutralize) the “bad components”. We refer to these “good components” as a sacrificial media, meaning they become depleted as they treat the water. If water has too high a TDS, it becomes difficult to dissolve those good components into the water and special sacrificial media or equipment is needed.
TDS is also used to figure out if certain equipment is working. Equipment such as reverse osmosis systems take out a very wide range of dissolved minerals/organic material in water to give homeowners nearly purified water. On these systems, if the treated water has a much lower TDS than the raw water, we know the equipment is working even if we don’t know what exactly it is removing.
How high of a TDS is too high? Well that depends. Water has the ability to dissolve different levels of matter. For instance, water has trouble dissolving calcite (the standard media in a neutralizer) once the TDS is above 600ppm. Magnesium oxide is a much more potent (and expensive) media to add to a neutralizer but does not have a problem being absorbed by water, even with a TDS well over 600ppm. That is why treating water is so much fun! Every water quality test results in different factors that we must take into account when determining which equipment is right (or wrong) for a plumbing system. TDS may not be as damaging as acid, but if it is ignored it can certainly make water treatment equipment ineffective. Check back next week as we explore what a neutralizer is and how it works!