The utility will use the proceeds to finance its investment plan and to reinforce working capital.
President Vizcarra moved quickly to use special legislative powers to authorize the funding.
The bill was approved in principle by a committee of the lower house and combines two previous proposals.
A water bill was being drafted by the former members of the committee on the environment and climate change, whose term expired last month.
The governments of La Pampa and Mendoza provinces have 90 days to reach an agreement.
The utility invested some US$4mn to increase the treatment rate in the city in Brazil's Minas Gerais state.
The former CEO of the disgraced Brazilian construction giant claims that some of its bribery payments were channeled through Argentine firms.