Start by finding the closest cold water line. You may need to drill a hole through the floor or wall to reach the pipe, and if you feel unsure about this, I recommend hiring a professional plumber who can help. Once located, shut off the water and drain the pipe by opening the cold water faucet.
Next, connect a saddle valve to a clean section on the pipe and tighten its clamps, so it is firmly connected. Screw the valve in to pop a hole in the pipe by slowly turning the valve’s handle clockwise. Next, connect ¼” copper piping with a compression joint.
Once this is secure, you can turn the water back on and open the saddle valve to rinse through the copper piping into a good-sized bucket. Finally, close the valve.