Vietnam has 2,360 rivers with an average annual discharge of 310 billion m³. The rainy season accounts for 70% of the year's discharge. Most of the country's urban water supply systems have been developed without proper management within the last 10 years. Based on a 2008 survey by the Vietnam Water Supply and Sewerage Association (VWSA), existing water production capacity exceeded demand, but service coverage is still sparse. Most of the clean water supply infrastructure is not widely developed. It is only available to a small proportion of the population with about one third of 727 district towns having some form of piped water supply. There is also concern over the safety of existing water resources for urban and rural water supply systems. Most industrial factories release their untreated wastewater directly into the water sources. Where the government does not take measures to address the issue, most domestic wastewater is discharged, untreated, back into the environment and pollutes the surface water.