I also have trouble believing in the profitability of the dual network ...
Already a minimum quality criterion should be established for the "non-potable" water delivered. Is it water from the river directly, with coarse filtration, or "clean" water not drinkable according to European laws but which would be considered drinkable by many people in other countries?
The minimum criteria (valid or not) are already established so question settled
If it is raw water without treatment, will people accept a variability in the quality of this water? there is always a complaining that it is too expensive even when it's free when the quality of what we provide them drops ... (and there it would not be free)
The so-called drinking waters are all treated so a settled issue too.
In the end we would end up with 2 network, one for drinking water that would be little used,
On the contrary ! In which cases is this drinking water used? For the food, the dishes, the care of the body does all that relates to the direct hygiene, possibly the watering of the vegetables of the garden. But laundry, toilets, watering cars, etc ... do not need to be drinkable
so with a risk of stagnation in the network and all that implies and another for water finally almost drinkable, so double investment, double maintenance, double statement and billing, with also a double network in housing and building for lead to a risk of error or a gas plant on the water points where the two networks will be available (when we already see what the law requires for rainwater networks ...)
This is only a problem of technique, not politics! The current losses of the network are related to the age of the cast iron pipelines which degrade, oxidize with time, this is no longer the case of the networks in "plastic" much more flexible to the solicitations of the ground. On the other hand, all the wastewaters no longer require any treatment, which is expensive and polluting. Finally, it is not a question of changing everything in one block, any more than the current networks have been done quickly. Similarly, lead pipes have not been banned on new homes and old houses. This is only technique! and therefore, people who refuse to drink tainted tap water, showers that stink of chlorine or ozone and other means would save the purchase of bottles of spring water or mineral.
Finally, when we see the crazy sums invested in the road network, the telephone networks and other modernities, a real network of really drinkable water would be derisory in comparison.
"We make science with facts, like making a house with stones: but an accumulation of facts is no more a science than a pile of stones is a house" Henri Poincaré