Urban Development Minister M. Venkaiah Naidu on Thursday said that urban infrastructure sector offers Rs.73 lakh crore investment opportunity for private sector and public-private partnership (PPP) investments over the next 15 years."Given the resource limitations of both central and state governments, private sector investments and PPPs are the chief instruments of resource mobilisation to build the much needed urban infrastructure in the country," Naidu said at an investment summit here.Naidu said that over and above the support committed by the central and state governments, ensuring basic urban infrastructure requires Rs.56 lakh crore, building 2 crore houses for urban poor needs another Rs.11 lakh crore and Rs. 6 lakh crore for building 100 smart cities.Expressing hope that private sector and PPP investments can be mobilized to address the infrastructure challenge, he said that 10 of the 20 smart cities announced last week have laid down clear road maps for mobilising PPP investments of about Rs.9,000 crore.Bringing out the gaps in urban infrastructure, the minister noted that 50 percent of urban households still do not have water connections.“These gaps hit the urban poor the most and developing urban infrastructure accordingly leads to inclusive urban growth besides enhancing productivity and quality of life,” he said.