Spurred by environmental concerns, the West Bengal Government is set to make it mandatory to have rainwater harvesting and solar power facilities in buildings. "Global warming and climate change are threatening us. We must, therefore, have greenhouse concepts like solar power and rainwater harvesting in new buildings. I am talking to my urban development minister to include these in the Municipal Act so that it becomes mandatory for all,' Chief Minister Buddhadeb Bhattacharjee said today. Inaugurating the 'Realty Expo 2008' of the Confederation of Real Estate Developers Association of India (CREDAI), he described paucity of housing as a national problem and said his government was stressing on construction of housing projects both by the government, private players and through public-private partnership (PPP). With the PPP model having been successfully implemented in the state's housing sector, the government now wanted the private players to take up construction of related infrastructure like roads, bridges and flyovers, he said. Pointing out that Rs 15 crore had been collected towards construction workers' welfare after the government made it mandatory for real estate developers to contribute to it, the Chief Minister appealed to private developers for greater contribution towards the welfare fund.