Safe water:
Safe and clean water should have TDS below 500 and PH between 6.5 and 8.5. generally ground water will have ph of 7. Between 7.5 and 8.5 considered as Alkaline water.
These days RO and other water purification machines are wasting so much of water but still giving unsafe water.. many areas RO water gets below 5 PH though they maintain TDS less than 50.
Generally rain water is TDS 20 to 30 and PH 7.5, which is perfect drinking water. There are natural methods to purify water.. eg. To reduce TDS use Amla (usiri kaya / nalli kaya).
Purifying Herbs
As mentioned before, BIS standards specify that drinking water should have a TDS of less than 500 ppm. Vetiver roots and the bark of the Indian gooseberry tree (Amla or Nellikkai) are capable of reducing TDS by half and help make the water potable. These herbs also vastly improve its taste.
The seeds of the Strychnos potatorum tree (Thethankottai in Tamil), also called the clearing nut tree are used to remove sediment or turbidity from drinking water. The seeds are rubbed on the inside of the water storage vessel and then filled with water. The seeds are natural coagulants that help the sediments settle down at the bottom of the vessel.
The search for safe drinking water is as old as human existence itself and the purpose of this article was to illustrate the fact that many natural, low-cost methods are known in India. Through this series, I hope to inspire many of you to explore these natural and innovative ideas, and think beyond what is now commonly available in a store as a water solution.
Coper pot:
storing water in a copper pot overnight kills several pathogens and that this ancient Indian water purification idea has also been corroborated by several recent studies The health benefits of copper water mentioned in Ayurveda though have not been extensively studied in recent times. For instance, copper has anti-inflammatory properties and helps with arthritic pains. Copper is also an anti-oxidant, prevents cell damage and ageing
solar cleaning system: http://www.thehindu.com/features/homes-and-gardens/green-living/purified-naturally/article5507791.ece
following info as per WHO:
TDS:
GENERAL DESCRIPTION
Identity
Total dissolved solids (TDS) is the term used to describe the inorganic salts and small amounts of organic matter present in solution in water. The principal constituents are usually calcium, magnesium, sodium, and potassium cations and carbonate, hydrogencarbonate, chloride, sulfate, and nitrate anions.
Organoleptic properties
The presence of dissolved solids in water may affect its taste (1). The palatability of drinkingwater has been rated by panels of tasters in relation to its TDS level as follows: excellent, less than 300 mg/litre; good, between 300 and 600 mg/litre; fair, between 600 and 900 mg/litre; poor, between 900 and 1200 mg/litre; and unacceptable, greater than 1200 mg/litre (1). Water with extremely low concentrations of TDS may also be unacceptable because of its flat, insipid taste.
ANALYTICAL METHODS
The method of determining TDS in water supplies most commonly used is the measurement of specific conductivity with a conductivity probe that detects the presence of ions in water. Conductivity measurements are converted into TDS values by means of a factor that varies with the type of water (2,3). The practical quantitation limit for TDS in water by this method is 10 mg/litre (M. Forbes, personal communication, 1988). High TDS concentrations can also be measured gravimetrically, although volatile organic compounds are lost by this method (4). The constituents of TDS can also be measured individually.
http://www.who.int/water_sanitation_health/dwq/chemicals/tds.pdf