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‘Watershed conservation can benefit 700 million people in 100 big cities’ (downtoearth)

Which are the top five cities in the world that face water stress?

In terms of water quantity risk, five of 15 major Asia Pacific cities—Shenzhen, Taipei, Singapore, Tokyo and Jakarta—are under stress and at risk of water shortage. One in three cities faces water stress on a global scale. In terms of quality, a majority of Asia Pacific cities suffer from high water source pollution, especially sedimentation.

Lower income cities face a greater challenge since their water infrastructure is generally less developed when compared to that of higher income cities. This means they are more likely to be water-stressed. Lower income cities in many parts of the world also have high population densities in their source watersheds, which makes the task of protecting their water sources harder.

What are the solutions to the problems faced by these cities?

One in four cities globally would see a positive return on investment from investing in watershed conservation. The five conservation strategies for cities with most cost-effective investment potential are forest protection, reforestation, agricultural best management practices, riparian restoration and forest fuel reduction.

Ten of 15 major Asia Pacific cities have high to medium potential for significantly improving their water quality through conservation strategies such as agricultural best practices and river bank (riparian) restoration. The solutions can improve the water quality for 700 million people living in top 100 large cities of the world.

Indian cities suffer from high pollution, but many hold high to medium potential for cost-effective watershed conservation. Mumbai is one city that can reduce sediment and nutrients from its water sources by 10 per cent through solutions such as agriculture best practices, subsequently lowering its water treatment costs by an average of five per cent.

Tell us about the urban water report.

Top global cities are facing challenges in managing drinking water supplies. They are struggling to control water stress, both quality- and quantity-wise. We have recently come out with a report which looks into these challenges. In the study, we have looked at the opportunity for source watershed conservation to help alleviate these challenges, paying special attention to water quality issues.

Our report “The Urban Water Blueprint” and interactive website serve as tools for decision-makers in evaluating water quantity and quality risks across the world’s largest cities, the steps cities have taken to overcome water stress, and the cost benefits of incorporating natural solutions.

Your study says that to cope with demand for clean water supply in large cities, there is huge inter-basin transfer of water where water from one river is transferred to another. Is another option available for secured water supply?

Broadly speaking, there are two types of solutions. First, cities can try to get more water by expanding surface supplies, increasing use of groundwater or desalination. All of these can be expensive and have limited scope for help. Second, cities can try to use the water they have more efficiently. Many cities waste almost half of their water supply through leaking pipes and other infrastructure. So there is tremendous scope for increasing municipal water use efficiency.

Can you cite a case study to explain your solution?

According to a report, Srinagar might see a high return on investment by reducing erosion from agricultural lands. The city draws a significant portion of its surface water—121 million litres per day (MLD)—from the Sindh river at two intake points located close together. The upstream contributing area of the sources is 1,120 hectares, and is predominantly (94 per cent) cropland. Assuming a conventional treatment plant sequence, treatment costs for only this 121 MLD of its water supply might be US $1.8 million per year.

Investment in agricultural best management practices (BMPs) at the sites would help get rid of the most sediment and phosphorus. Around 32 hectares of agricultural BMPs would need to be installed to remove 10 per cent of sediment and phosphorus. In other words, working on 3 per cent of the cropland is sufficient to reduce sediment and phosphorus in the basin by 10 per cent.

Such an investment clearly seems to be the one with a positive return on investment where the benefits of conservation are almost nine times the cost.

How will this conservation practice cut down the operation and management costs of the water supply systems?

We do not have data specifically for Indian cities. In the report, however, we have shown the global average where a 10 per cent reduction in sediment or phosphorus leads to five per cent reduction in the operation and management costs of a water treatment plant.

What message does your study have for Indian civic authorities on urban water supply?

The message is that source watershed conservation activities can deliver real cost savings to Indian cities while helping make urban water supplies cleaner.

Urban water blueprint: mapping conservation solutions to the global water challenge


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