12. Total Dissolved Solids (TDS) & Activated Carbon Filter
Total dissolved solids (TDS) is a measurement of the total amount of dissolved inorganic compounds in water. It is determined by an instrument that measures the ability of water to conduct electricity. As the concentration of inorganic compounds increases, water becomes a better conductor of electricity. The test does not determine which specific compounds are in the water, only the total concentration. These instruments will typically display the test results as parts per million. It is normal for tap drinking water to contain inorganic compounds. Typically, these would be calcium bicarbonate, magnesium bicarbonate, potassium bicarbonate and other possible compounds. These are beneficial minerals that are commonly found in Natural Mineral Water.
Only Reverse osmosis and distiller type systems can remove most of the inorganic compounds in water, which reduces the electrical conductivity of the treated water. Adding an ion exchange resin to reduce the inorganic ions in water can also reduce TDS. TDS instruments are very useful to determine if these types of products are performing well.
Since, activated carbon does not remove most inorganic compounds from water; TDS is not an effective way of measuring the product performance. In fact, carbon adds some trace minerals (inorganic compounds) to the water. As water passes by carbon, trace amounts of some inorganic compounds dissolve in the water. These compounds can be potassium bicarbonate, sodium bicarbonate and calcium carbonate. Therefore, activated carbon can increase a measurement of the TDS. This effect is more pronounced with a new filter. As a filter is used this effect decreases over time as these inorganic mineral materials reduce in amount.
The reason that activated carbon makes such a great material for water filters is that it is natural and effective at removing many toxins from the water, such as volatile organic compounds and chlorine, without the use of chemicals or stripping the water of beneficial minerals. Organic compounds do not usually change the electrical conductivity of water; therefore, a TDS meter will not be able to measure them, and hence TDS is not an accurate indication of water quality.