Green groups have criticised police for wasting at least 200 tonnes of water to fill the plastic barriers used during the three-day visit of President Hu Jintao last weekend.
About 200 of the two-metre-high barriers, each one weighing two tonnes when filled with water, were placed around the Convention and Exhibition Centre and Grand Hyatt hotel in Wan Chai as part of security for Hu's visit.
About one tonne of fresh water was needed to fill each barrier and afterwards they were emptied at the scene before being removed because they were too heavy to move when full.
Green Power chief executive Man Chi-sum said the total amount of water poured away could have supplied more than 900 adults, or about 300 families, with water for one day.
'Of course it is wastage,' he said.
'There is a shortage of water in Hong Kong and the whole world. Less than 1 per cent of the world's water resources is drinkable.'
Man said the police should have used processed sewage to fill the water barriers, or recycled the water for cleaning or watering plants.
Friends of the Earth chief executive Chan May-ling agreed.
She said Hong Kong people on average used 220 litres of water a day, far more than people in many other modern cities like London and Paris, who used less than 150 litres.
She said the public and police were guilty of wasting water and the government lacked a progressive policy to resolve the water crisis.
'The government does not see water as a resource that needs protection. It sees water as a commodity. It does not care how much is wasted,' Chan May-ling said.
The use of the barriers themselves also drew criticism from protesters, who objected to being surrounded by them, saying it was a tactic to suppress opposition voices.
Andrew Shum Wai-nam, an organiser of the June 30 protest outside the exhibition centre, said he would lodge a complaint with the police next week about the surrounding of protesters with the barriers and the use of large canisters of pepper spray on them.
A police spokesman said the force had a responsibility to ensure state leaders' safety during visits to the city and would make appropriate security arrangements, including using water barriers, which had to be moved quickly after the protests.