Problems with water, What must give the guarantee

Hello am new here in the forum and I also have a big problem. I bought a Volvo C30 not quite 1.5 years ago. from the beginning I had problems with this car – I probably got one of these Monday cars now since this time with water that comes both in stand as well as when driving at the doors in the car. have already water stains on the seat. Now I want to ask what such a new car guarantee has to give. Have I claim to a new seat and what if the workshop does not get the problem with the water in the grip (was already 3 or 4 times there) thank you already for your answer