Dear Igor, Many thanks for ...

Dear Igor,

Many thanks for your interestinganswer.

It should be noted that dual water system is not necessarily dual water network.

In the case that quality of available water does not meet required standard of drinking water but can be accepted for other domestic consumption (e.g. bathing, dishwashing, …) people may use bottled water or take drinking water from local water kiosks, or may use domestic water treatment  plant to provide  water for their drinking (and perhaps cooking) need. In all mentioned cases drinking water is separated from other domestic consumption by a "non-conventional dual water system".

Based on this definition, many cities and villages use non-conventional dual water system. For example in some cities and villages in Asia and Africa, where  TDS or Nitrate level of network water is higher than the drinking standard value, drinking water is distributed by local water kiosks and the lower-quality water of main pipe network is used for other domestic consumption (e.g. bathing, dishwashing, …). In this case, main concern is not about drinking water but about using the non-drinking part which obviously doesn’t have quality of water drinking standard (e.g. WHO Guidelines forDrinking-waterQuality, 2011).

Suppose people take shower with water which has high level of Nitrate or TDS value, is it dangerous for their health in short or long time? Does anystandard of water quality exist for this? Same questions exist about water quality of dishwashing.