If and when zero-COVID ends, individual testing in China could collapse the same way it’s collapsed in other countries. And there isn’t a countrywide wastewater monitoring system to pick up the slack in data. Yet. “To cope with the future challenges in public health emergencies, it is vital to monitor sewage,” a team led by Ying Zhang, an environmental engineer at China’s Fuzhou University, explained in a new academic study.

Part of the problem is that, for all its rapid economic growth over the past generation, China is still a developing country—and its development is uneven. That’s apparent in the sewer system. “The allocation of the pipeline across the whole country is unbalanced,” Ying’s team wrote. Drainage is concentrated in the industrial east at the expense of the rural west, leaving potential gaps in surveillance.

And the pipes that do exist aren’t always well-built. “Because the operation, management and maintenance of the drainage system have not drawn much attention in China, serious problems within the drainage system occur in many cities, such as leakage, overflow and blockages.” Blocked and leaky pipes can corrupt samples.