That depends on which pipe it is. Are you talking about piping above the water heater or somewhere else? If it is a copper flex line, you can do it yourself if it is threaded at both ends. If it is soldered where it connects to the house plumbing, you’ll probably need a plumber. Consider turning off the water pressure to the water heater when you’re not using hot water. That may get you through to Friday when plumbers are back at work.