Like all other animals, rats need food, water, and shelter to stay alive. Food isn’t much of a problem; rats will eat anything they can find, and their powerful sense of smell enables them to sniff out food sources from some distance. However, if a rat can’t find food for more than a week, it is in serious trouble. Water is a different matter.
While rats require significantly more water in their diets than mice, both rats and mice can extract water from foods more efficiently than people can. Food that seems dry to us can still provide rats with vital moisture. If a rat has access to food, but no water supply, it can still live for up to a month. The reverse is not true; with water but no food, a rat can’t last very long.
Rats like to build their nests close to reliable water supplies. This need for water is why rats are more likely to nest in sewers and pipes than mice. Mice can survive on just the water in their food. If they need to supplement this, they will often lick condensation off pipes. Even this meagre amount of liquid can make all the difference to them.
Removing rats’ access to water can form part of a strategy to encourage them to leave your property, but it won’t be enough on its own. Removing access to food causes a much bigger problem for them. In ideal circumstances, rat’s food is an important water source.
If they still have easy access to water, it will take some time before they’re forced to go and scavenge elsewhere. But if neither food nor water is available, rats will usually leave rather than waiting to starve to death.