Rats are a serious issue around the world. The UN considers them a severe danger to humanity similar to global warming. The UN stores food for emergencies, this food is often infested by rats and the destruction numbers in the billions per year. Rats were once treated by the governments of major cities like new york. The team was called the rat task force and would bait public places, parks, subway stations and sewers as well as public buildings. This ended in 2008 when the housing crisis causes an economic crash. This resulted in governments cutting costs to the extreme and one of the first things to go was the rat task force. So if you have rats that do not rely on the government, call a professional to deal with it permanently.
Rats are burrowing animals. They are also very good swimmers as far as the common Norway rat is concerned. The Norway rat came to America on ships often from Norway. Those rats have spread across the world and have no direct predators other than predatory birds. By burrowing they avoid this danger and with incisors that continue to grow for their entire lives, they can chew through essentially anything if given enough time. This is the main reason you will see rat activity primarily in your basement. The most common sign that you have rat activity is feces. The feces of rats is large than mice. A mouse’s feces is about the size of a short grain of rice. A rat’s feces is much large and smells much worse.
Once you are aware that you have a rat infestation you should deal with it directly on both the inside and the outside. Rats do not live inside of human homes. They are not small like mice and know you will eventually find them. They live on the outside of the house, on the property in burrows along with structures like sheds and under decks. They will enter your home at night to find food and then vacate the exterior. The good news about this is that treating them on the inside is limited to baited snap traps. On the exterior, you must place large bait stations with domestic grade rodenticide. If you want a stronger poison you will have to call a professional.
The way to end the interior infestation permanently is to inspect your house for opening. This can be anything from a tiny foundation gap to a loose plastic wall vent. Old houses are most affected as they have been altered through the years and sometimes not very well. Plumbing vents are common and are easy to access for rats. So seal those openings as best you can or call a professional to seal them for you.