NEA officers use chemical treatments in drains as part of a comprehensive mosquito control strategy. While source reduction is the key to prevent mosquito breeding, chemical control can complement the mosquito control effort during outbreaks.

The chemicals used in drains include Bacillus thuringiensis israelensis (Bti) and temephos (a sand granular insecticide). These substances specifically target and kill mosquito larvae in areas where water cannot be completely removed, such as drains, roof gutters, and gully traps. Temephos, which NEA officers apply to drains, is the same type of granular insecticide recommended for homeowners to use in flower vases and other water containers.

These treatments are safe for public health and the environment. The active ingredient of the insecticide does not have a long residual effect on the environment, and the concentration used is low and deemed safe by the World Health Organization (WHO).