I am no expert on El Alto and La Paz's water situation, but I think there are a few different issues that have to be sorted out.
Firstly, I am aware that the cost of source/bulk water sources was the ultimate cost behind things - all the way back to the protests El Alto/La Paz (and Cochabamba, really) in the early 2000s. Public or private this is a borne cost by any utility that has to function in these cities.
The question I have is to what extent the government hamstrung itself by not investing in source water for the utilities 15 years ago? Also, to what extent is allocation across sectors an option? Surely agriculturally used water is not at as high a per-unit value use as urban drinking water....?
Additionally, even though La Paz has 95% of the population connected to the utility, surely there is room for policies that increase connections in El Alto, where those infamous 'areas no servidas' /unserved areas under the early 2000 concessions existed.
I'm not saying that there are any easy answers, but water service delivery in these cities show so many lessons to learn from, be they investing in source water supplies or getting more people connected (so they don't pay resale prices). I hope that those policies that made resale by utility-connected households and communal standpipes illegal in the 2000s don't exist anymore...?
Lastly, to what extent has pricing been a problem. While there is a need for the social tariff (often at below-cost), there must be either cross-subsidies from wealthier paying consumers and/or a tax base that fills the gaps that the subsidies present on the balance sheets.
It's not sexy or politically correct to say this, but utilities have to function like a business. Having said this, the government can and should support input costs and support subsidized rates.