GS3 not staying connected to wi-fi

[SSDCarroll3]

I just got this phone and this is my first smart phone, so I don't know if I am doing something wrong. My phone keeps dropping the wi-fi connection, regardless whether I am at home or at work. If I check the available wi-fi networks it shows a strong signal strength & then I'll connect again & then a few minutes later, it is disconnected. It is very frustrating. What good is having wi-fi if you can't rely on it?

Thanks in advance.