Unless rainwater enters the rain barrel or tank/cistern through pipes that are connected directly to the top or side of the rain barrel or tank/cistern, you must ensure all water passes through a tank screen at tank entry point. The tank screen must include a non-corrosive screen of not more than 0.04" to keep mosquitoes and pests out.
Whilst tank screens will further filter out leaves and debris, rain heads should be fitted at each downspout that supplies water to the tank/cistern, and first flush water diverters should be fitted ‘upstream’ of the tank screen to optimize water quality. The tank screen should provide the final point of protection not the only barrier for leaves, debris and pests. Tank screens must be secured with screws to the tank to ensure it remains in place.