We thank Mr Steven Lo Chock Fei for his feedback (Oiling stagnant water can't be permanent solution; March 14).

The key strategy to mosquito control is source reduction. Infrastructure, such as drains, needs to be maintained regularly to prevent water stagnation and the breeding of mosquitoes.

Water stagnation can occur if the drain is choked, perhaps with litter, or when there is damage due to wear and tear.

When the National Environment Agency comes across damaged drains, it will work with the relevant stakeholders to rectify them as a more permanent control measure.

However, as it may take some time for such repair works to be carried out, anti-malarial oil is usually applied in drains as an interim measure to prevent mosquito breeding. The use of anti-malarial oil, which is biodegradable, in drains is permissible and not harmful to the environment.

Tony Teo

Director, Environmental Public Health Operations

National Environment Agency