Ants in the house can be carpenter ants or regular old household ants. If your ants avoid regular food to get to some water they could be carpenter ants: campanotus pennsylvannicus.
Carpenter ants use the plumbing vent stack as an expressway from the basement to the attic. (They share it with the mice.) There is damp wood available in the attic behind the gutters or in the rotting roof boards that are replaced when a house is re-roofed. They also have damp wood available under a bathtub due to worn out caulking or a faucet leak. Sometimes a little sawdust on the floor around the stink pipe in the basement can indicate infestation of carpenter ants.
If these were regular household ants, we would have recommended using Terro ant killer. It is syrup (with borax, not poison) applied to cardboard scraps that the ants carry back to the nest. Usually it wipes out the whole colony in about three days. This product is not recommended for carpenter ants but works great for sweet eating ants.
Getting rid of carpenter ants can be very difficult. The main reason is you have to locate the nest in order to kill the queen.
If you do not kill the queen she will take some eggs, a few workers, and run to safety. She will then establish a new nest in some damp lumber elsewhere. It could be years before you see another carpenter ant. If you do not kill the queen, you will only be hiding the problem.
Enforcer Products makes Cypermethrin, available at most hardware and garden centers for about $8.99. It is a concentrate that produces about two gallons of killer. That should be more than sufficient to eliminate a colony of carpenter ants as long as you kill the queen.
Killing ants is not the only thing you have to do. You also have to rid your house of all the potential homes for the ants. If they do not have food and habitat they will not stop and visit. Places to check for ants are; leaks in the plumbing, in and under windowsills, wood behind gutters (especially after all our ice dams), and outside woodpiles.