"Establishing a right to water, therefore is another way of recognising the right to life already enshrined by the United Nations - recognise water as a human right," Mamani said.
The theme of this year's World Water Day is water scarcity, a problem primarily driven by population explosion, chronic wastage and pollution.
Residential water consumption is 10-20 litres per person per day in sub-Sarahan Africa. It is 350 litres in North America and Japan.
Lack of safe water and sanitation is the world’s single-largest cause of illness.
In some areas, 30 to 40 per cent of water use goes unaccounted for due to water leakages in pipes illegal tapping.
In 2002, 42 per cent of households worldwide had no toilets and one in six people had no access to safe water.
Individuals need 20 to 50 litres of clean water every day for all their needs.
Source - UN
The UN estimates that by 2025 two-thirds of the planet's population will be living with economic, social, or environmental problems caused by water shortages.
North Africa, the Middle East and West Asia are expected to be among the worst afflicted regions.
Experts say global warming will also take its toll on supplies.
A draft report by the UN's Intergovernmental Panel on Climate Change says a global temperature rise of 2C (3.8 F) by 2100 would place up to two billion people in a position of "increased water scarcity".
A rise of 4C (7.2 F) would affect as many as 3.2 billion people, the draft calculates.
In a message to the assembly, gathered at the European parliament in the Belgian capital, Alfonso Pecoraro, the Italian environment minister underlined the need to recognise this "semi-precious" resource as a "public good".
The assembly set the international recognition of the unique status of water as its primary goal.
Riccardo Petrella from the World Water Contract group said: "Our target is December 10, 2008 - the 60th anniversary of the Universal Declaration of Human Rights - for the UN's human rights council to recognise water as a human right."
Petrella that water "is essential for all forms of life" and called for public service providers to unite and bring an end to its "marketing".
"Public water suppliers account for 80 per cent of world water supplies and they are letting the private sector, which controls 20 per cent, call the shots," he told the assembly, which met over three days and ended on Wednesday.
The World Water Assembly estimated that it would cost "less than 50 billion euros [$66bn dollars] per year" to provide the essential 50 litres of water per day "to each of the 1.2 billion humans who do not have it".
It plans to set its demands in a letter to heads of state, governments and the United Nations in an effort to convince them of the need to establish access to water as a new "human right".
The World Water Assembly for Citizens and Elected People describes itself as a group of elected representatives, civil society organisations, trade unions and citizens dedicated to water-related issues.