If you have a leak coming from a plastic o PVC water pipe it may be something you can fix yourself. Water can travel a long way before you see it dripping so you need to ensure you know exactly where the joint is leaking from before you start the repair. Firstly you would need to dry the area thoroughly and work out where the water is coming from, whether it is from the water pipe or the joint.
Once you have located the source of the leak, you need to shut off the water supply for the affected area alternatively you can shut off the water mains supply if it is easier.
To fix the leak if you are comfortable in doing so, you can remove and replace the affected section of the pipe. This may require the use of tools and equipment to cut the pipe, if that is the case you can do a temporary fix by using rubber or silicone repair tape which is easy to use. Repair epoxy is also another easy option you can use around plastic pipe joint leaks as it can mould to fit the shape of the joint.
If the water pipe is leaking and not the joint then the process is pretty much the same as above for the joint. You can also use a rubber and hose clamp for a temporary repair before you call out a plumber for a more permanent fix.