How can contamination of drinking water occur from sewage even in a covered drainage system?

Contamination of drinking water from sewage can occur even in a covered drainage system due to several factors:

1. Cross-Connections: In some cases, there might be cross-connections between the drainage system and the drinking water supply lines. This can happen due to faulty plumbing, improper construction, or accidental damage. If there's a break or leakage in the sewage pipes, the contaminated water can enter the drinking water system through these cross-connections.

2. Backflow: Backflow occurs when the pressure in the drainage system exceeds the pressure in the drinking water supply. This can happen during heavy rainfall or when there's a blockage in the drainage pipes. When backflow occurs, the contaminated water from the drainage system can flow back into the drinking water pipes.

3. Seepage and Leakage: Even in a covered drainage system, there might be points where the pipes are damaged, cracked, or have loose joints. This can lead to seepage or leakage of sewage water into the surrounding soil and groundwater. If the drinking water source, such as a well or aquifer, is located near the contaminated area, it can become polluted.

4. Overflow: During heavy rainfall or when the drainage system is overloaded, there's a risk of overflow. This can result in raw sewage spilling onto the ground and mixing with surface water, which can eventually contaminate nearby drinking water sources.

5. Poor Maintenance: Inadequate or improper maintenance of the drainage system can contribute to contamination. If the pipes are not regularly inspected, cleaned, and repaired, blockages and leaks can occur, increasing the risk of contamination.

To prevent contamination of drinking water from sewage, it's crucial to ensure proper design, construction, maintenance, and regular inspection of the drainage system. Additionally, there should be strict regulations and monitoring to prevent cross-connections and enforce proper plumbing practices.