TDS, which stands for Total Dissolved Solids, refers to the amount of organic and inorganic dissolved substances that may be found in your water, such as minerals, metals and salts. Essentially, it is everything present in water other than pure H2O and suspended solids. TDS can be from natural sources such as dissolved rock or from man-made chemicals such as Volatile Organic Chemicals (VOC’s).
Often, a major component of TDS is hard and soft minerals. Because water is naturally slightly acidic, as it travels through the rock formations in the ground a small quantity of rock is dissolved into a liquid form. These dissolved minerals include calcium, magnesium, chlorides and silica.
Total Dissolved Solids are measured as parts per million (ppm), and it is worth noting that Federal drinking water standards recommend a limit of 500 ppm. It is also worth noting that the national average is probably in the range 300-350 ppm for the United States. In some coastal areas and areas with heavy limestone deposits TDS can be well over 1400 ppm. The lower the TDS, the more pure the water is.
The concept of parts per million may be difficult to visualize, but the same measurement can be stated as “milligrams per liter” when you discuss mineral content. If you evaporate one liter of water with mineral content and collect the dried mineral powder, it can be weighed in milligrams. A water sample with 50-70 ppm will contain enough dried mineral content to equal the size and weight of about one generic aspirin tablet.
What are the effects of TDS and how can it be treated?
TDS is a secondary drinking water standard by the USEPA which means it generally is not a health hazard. However, high TDS creates a variety of problems for foodservice operations:
- It affects the taste of water and beverages, and can mean that sodium, calcium, chloride, and magnesium may all be detectable in your final product. Depending on the quantities and combinations of the dissolved materials, water can taste alkaline (bitter), salty or metallic.
- Hardness, normally a component of TDS, can create scale in equipment that heats or freezes water such as coffee brewers, ice machines and combi ovens.
- It can cause your ice machine to produce fast melting, cloudy, soft ice.
- High TDS can cause iced tea to become cloudy after brewing.
- It will reduce the carbonation in your fountain beverages.
- During coffee and espresso brewing, solids are extracted from the coffee grounds. Without consistent TDS levels the quality of coffee and espresso can range greatly from strong and bitter to weak and underdeveloped.
With nearly all foodservice equipment, some TDS is desired, depending on the application. The mineral content in TDS is what gives water flavor. Without it, water would taste flat (this is one reason why straight RO water is not used for beverages). For coffee and espresso, a TDS of 150-200 ppm is best for proper flavor. For drinking water and fountain beverages, a TDS of up to 500 is acceptable. For boiler-based steam ovens, TDS should be kept very low, less than 100 ppm (but not too low or the probes in the boiler won’t be able to detect the water levels). Check your steam warranty for the recommended TDS levels.
Many types of dissolved material will pass through mechanical and carbon filtration, and often require treatments such as reverse osmosis or water softening.