The two met at Halonen's official residence at Mäntyniemi following Wednesday's Baltic Sea Action Summit at Helsinki's Finlandia Hall.
"Thanks to your active role, a water purification plant has been built in St Petersburg. This work will be continued in St Petersburg and Kaliningrad," Putin pledged.
Halonen, meanwhile, thanked Putin for his participation in the conference. He replied that Helsinki is an excellent meeting ground for discussion.
Nord Stream Decision Due Soon
At the conference, Putin promised to beef up water purification efforts in St Petersburg and Kaliningrad. He also defended the Nord Stream gas pipeline project. The 1,220-kilometre-long offshore natural gas pipeline is to stretch through the Baltic Sea from Vyborg, Russia to Greifswald, Germany.
Finnish Prime Minister Matti Vanhanen told Putin that Finnish environmental authorities would announce their decision on the last of the three licenses required for the construction of the pipeline "within days". The Finnish government already gave the project its seal of approval last autumn.
"As far as natural gas reaching Europe by pipelines is concerned, this gas will always be cheaper than liquefied gas," said Putin.
Putin added that despite international efforts to find green energy solutions, dried dung and other alternative sources could not replace fossil fuels in coming decades.
"Fortunately or unfortunately, neither solar power nor firewood nor dried manure can replace hydrocarbons in the next 20-25 years," Putin told a joint news conference with Vanhanen.
Putin also held talks with Latvian President Valdis Zatlers and Norwegian PM Jens Stoltenberg in Helsinki on Wednesday.