While it is possible in some extremely rare cases that polluted water could be used for redundant uses, it is unlikely that water containing the vast number of contaminants possible in this post-industrial age could be viewed as 'useful'. The reason why is that every year source and ground waters around the globe face a growing number of contaminants that require advanced treatment and source protections.
For example, public utilities use chlorine to kill disease-causing microbes and waterborne diseases like giardia. But pollution and contaminants has led some municipalities to use more chlorine to disinfect their water supplies. Chlorine isn't dangerous in and of itself, but it can react with organic material in the water supply to create some questionable byproducts. Some of these disinfection byproducts (sometimes called DBPs) have been linked to birth defects and increased risk of miscarriage. The best way to reduce these byproducts is to reduce pollution at the source, thus decreasing the need for so much chlorine.
Your drinking water can become contaminated at the original water source, during treatment, or during distribution to the home. If your water comes from surface water (river or lake), it can be exposed to acid rain, storm water runoff, pesticide runoff, and industrial waste. This water is cleansed somewhat by exposure to sunlight, aeration, and micro-organisms in the water. If your water comes from groundwater (private wells and some public water supplies), it generally takes longer to become contaminated but the natural cleansing process also may take much longer. Groundwater moves slowly and is not exposed to sunlight, aeration, or aerobic (requiring oxygen) micro-organisms. Groundwater can be contaminated by disease-producing pathogens, leachate from landfills and septic systems and careless disposal of hazardous household products.
One branch of contaminants that would be hard pressed to be useful in improving the quality of your drinking water is microbial pathogens .Microbial Pathogens in drinking water are serious health risks. Pathogens are disease-producing micro-organisms, which include bacteria (such as giardia lamblia), viruses, and parasites. They get into drinking water when the water source is contaminated by sewage and animal waste, or when wells are improperly sealed and constructed. They can cause gastroenteritis, salmonella infection, dysentery, shigellosis, hepatitis, and giardiasis (a gastrointestinal infection causing diarrhea, abdominal cramps, and gas). The presence of coliform bacteria, which is generally a harmless bacteria, may indicate other contamination to the drinking water system.
Another category of troublesome contaminants are organics. People worry the most about potentially toxic chemicals and metals in water. Only a few of the toxic organic chemicals that occur drinking water are regulated by drinking water standards. This group of contaminants includes: Trihalomthanes (THMs), which are formed when chlorine in treated drinking water combines with naturally occurring organic matter. " Pesticides, including herbicides, insecticides, and fungicides. Volatile organic chemicals (VOCs), which include solvents, degreasers, adhesives, gasoline additives, and fuels additives. Some of the common VOCs are: benzene, trichloroethylene (TCE), styrene, toluene, and vinyl chloride. Possible chronic health effects include cancer, central nervous system disorders, liver and kidney damage, reproductive disorders, and birth defects.
Just like their contaminant cousins, inorganics also are problematic and not easily converted into something able to improve your quality of water. These contaminants include toxic metals like arsenic, barium, chromium, lead, mercury, and silver. These metals can get into your drinking water from natural sources, industrial processes, and the materials used in your plumbing system. Toxic metals are regulated in public water supplies because they can cause acute poisoning, cancer, and other health effects. Nitrate is another inorganic contaminant. The nitrate in mineral deposits, fertilizers, sewage, and animal wastes can contaminate water. Nitrate has been associated with "blue baby syndrome" in infants.
At the moment, our present science makes it rather unlikely that we will be able to take bothersome contaminants and make them work to improve your water quality, rather than bother you with negative side effects. While some waters can be reused in other environmental applications and possibly retreated, contaminated water remains a problem to be solved through progressive treatment options; both at the municipal treatment level and at the home.