The water contamination crisis in lanzhou is drawing to a close, but the psychological shadow it has cast, not only over the city itself but also other parts of the country, will take longer to fade away.

Oil leaks from a petrochemical plant in the vicinity of a water transport canal in 1987 and 2002 were said to be the culprits for the contamination. This has increased many people's doubts about how safe the tap water they drink every day can be.

If oil leaks a long time ago can contaminate a city's drinking water, what about the sewage many cities discharged directly into rivers or even ditches without being treated and the pollutants industrial enterprises have dumped wherever they considered it convenient?

About 70 percent of China's waterways have been polluted to different degrees, and major rivers such as the Yangtze and Huaihe are heavily polluted. Sixty percent of China's groundwater cannot reach the national standards for drinking water, according to the Ministry of Water Resources.

It is true that more than 3,000 sewage treatment plants had been constructed nationwide by the end of 2013, and more than 80 percent of them are reportedly operating. But repeated reports about how some of them are idle when they are not under supervision should propel local governments to tighten supervision over such plants. This will strengthen their role in reducing the harmful pollution.

Even if all the existing sewage treatment plants were running at their full capacity, we should not turn a blind eye to the fact that we are heavily indebted when it comes to environmental protection.

What has happened in Lanzhou points to the harsh reality that China is facing a double workload for environmental protection: not only to make sure all the sewage and industrial pollutants are treated before they are discharged, but also to rehabilitate the soil, waterways and groundwater that have already been polluted over the past several decades.

It will take a long time and painstaking efforts for the country to do both well. Of all the work that needs to be done, the priority is to protect the sources of drinking water. This should be placed high on working agenda of all local governments.

Empty promises without concrete action will hardly drive away the psychological shadow that water contamination accidents cast over the nation.