Total dissolved solids
[1] Generally, the operational definition is that the solids must be small enough to survive filtration through a filter with 2-micrometer (nominal size, or smaller) pores.
The term settleable solids refers to material of any size that will not remain suspended or dissolved in a holding tank not subject to motion, and excludes both TDS and TSS.
Runoff models have evolved to a good degree of accuracy and permit the evaluation of alternative land management practices upon impacts to stream water quality.
[7] This hydrology transport model is actually based upon the pollutant-loading metric called "Total Maximum Daily Load" (TMDL), which addresses TDS and other specific chemical pollutants.
The success of this model contributed to the Agency's broadened commitment to the use of the underlying TMDL protocol in its national policy for management of many river systems in the United States.
Hard water can cause scale buildup in pipes, valves, and filters, reducing performance and adding to system maintenance costs.
Typically, total dissolved solids are tested frequently in these applications, and filtration membranes are checked to prevent adverse effects.
For freshwater, oysters, trouts, and other high-value seafood, the highest productivity and economic returns are achieved by mimicking the TDS and pH levels of each species' native environment.
Because the threshold of acceptable aesthetic criteria for human drinking water is 500 mg/L, there is no general concern for odor, taste, and color at a level much lower than is required for harm.
Nevertheless, some numerical information is a helpful guide to the nature of risks in exposing aquatic organisms or terrestrial animals to high TDS levels.
Daphnia magna, a good example of a primary member of the food chain, is a small planktonic crustacean, about 0.5 mm (0.020 in) in length, having an LD50 of about 10,000 ppm TDS for a 96-hour exposure.
[12] In the Truckee River, EPA found that juvenile Lahontan cutthroat trout were subject to higher mortality when exposed to thermal pollution stress combined with high total dissolved solids concentrations.
