Bill et al,
World Health Organization to the rescue; but anything <500 ppm is good.
"TDS is a measure of Total Dissolved Solids in Water which comprise of inorganic salts, principally calcium, magnesium, potassium, sodium, bicarbonates, chlorides and sulfates, and small amounts of organic matter that are dissolved in water. TDS in drinking-water originates from natural sources, sewage, urban runoff, and industrial wastewater. Concentrations of TDS in water vary considerably in different geological regions owing to differences in the solubility of minerals.
According to WHO report on Drinking water standards, NO health-based guideline value is proposed for TDS in Drinking Water which essentially means that human body can ingest any amount of TDS in water without any health impact. Now the question is …Why high TDS is considered bad in Drinking Water?
The simple reason is the palatability or taste! Yes, you heard it right. High levels of TDS in drinking-water may have a certain objectionable taste because of salts. The palatability of water with a TDS level of less than 600 mg/liter is generally considered to be good; drinking-water becomes significantly unpalatable at TDS levels greater than 1200 mg/liter. Also, TDS may be high because of certain chemicals which are harmful and hence purification is required to eradicate them. However, this is not a concern in naturally available water. Thus, we can drink the water of any TDS level if it is devoid of harmful pathogens, chemical, and other unacceptable impurities.Hence…high TDS does not lead to any health problem. The presence of high levels of TDS may also be objectionable because of excessive scaling in water pipes, heaters, boilers, and household appliances.
Alternatively, water with extremely low concentrations of TDS may also be unacceptable because of its flat, insipid taste.Most purification techniques such as filtration, membrane processing or sedimentation aim to eliminate the impurities that form high TDS. Water is treated or purified to maintain palatability as well as purity in terms of microbial and chemical composition. It has nothing to do with TDS or mineral content. Purifiers in the market with TDS modulator or a Mineral Booster are just for marketing promotion for naïve customers and do not have any rationale behind it.
To know more about TDS in drinking water, go through the following research published by WHO.WHO Guidelines for drinking-water quality -2008