Bolivian President Evo Morales has said his country will file a suit against Chile over a water dispute at the International Court of Justice (ICJ).
Bolivia says it owns the Silala spring in a border region and that it is not being compensated by Chile for the use of its waters.
But Chile says it is an international waterway of shared use.
Bolivia had brought up another case against Chile at the Hague-based ICJ, demanding access to the Pacific Ocean.
The River Silala rises in Bolivia but flows down the Andes into Chile.
“We have decided as a pacifist country to go to The Hague so that Chile respects our water in Silala,” Mr Morales said.
Chile’s Foreign Minister Heraldo Munoz said the country could file a counterclaim.
“What is clear is that it is not only about the sea, now it is about the rivers and any other excuse to attack our country and its interests,” Mr Munoz was quoted by Efe news agency as saying.
Chile uses water from the river to supply mine operations and some northern towns.
In 2013, La Paz took the century-old dispute with Chile over access to the Pacific Ocean to the court, which has yet to rule on the issue.
Bolivia lost 400km (240 miles) of coast to Chile in a 19th-Century war and has been landlocked ever since.