Cockroaches can survive only about 1 week without water but can live for about 1 month without food.
This fact reveals a key anti-cockroach strategy: cutting off water is more effective than cutting off food.
Cockroaches are ectothermic and lose body water through spiracles on their body surface; in a dry environment, their survival time is greatly reduced.
Water sources for cockroaches in a household environment include: dripping faucets, pipe condensation, water in the evaporator pan under the refrigerator, standing water in plant saucers, pet water bowls, and even water stains on bathroom tiles.
Eliminating these seemingly minor water sources is one of the most effective non-chemical methods for cockroach control.
In a professional IPM strategy, the first step is often not spraying but having a technician conduct a thorough "water audit"—inspecting and repairing all leaks and wiping up all standing water.
The mode of action of diatomaceous earth is also water-related: it adheres to the cockroach's body surface, abrading its protective waxy layer and causing the cockroach to die from dehydration.