Most good slow drain will recommend replacing a gate valve regardless of its condition. The time to discover if it will work is not during a flood in your bathroom. If you have it replaced with a ball valve then check your water heater and laundry valves, too. Have them replaced at the same time with premium ball valves. Ball valve laundry bibbs make it easy to shut off the water to the washer after each use which may help to prevent floods in the future.
If you find that the water line repair leak is in the supply line you will need to replace it or simply tighten it. Start by turning the water supply off and then flushing the toilet to get rid of the excess water. Now use the towels to dry the area so that it is easier for you to fix the leak. Use a wrench to loosen the hexagonal nuts on the supply line at the main end as well as the one which goes to the flush tank. Now use the replacement supply line which you have and tighten the bolt at the supply end first. Now adjust the length that you will need for the pipe to reach the flush tank. Once you adjust the length use a knife to cut the extra length and then tighten the hexagonal bolt at the other end.
One other common design that is considered "washerless" was made famous by Delta and copied by several other makers. It uses little "cup" seals that fit over springs recessed in the back of the valve body. The springs press these "seals" against the cartridge and regulate the flow through little tapered openings in the cartridge. If you have one of these and it's dripping, changing these springs and seals will usually correct it. Here's a tip. Once you have the cartridge out of the way, insert a phillips screwdriver into the seal and pop both the seal and spring out. Stick the new ones on the end of the screwdriver to help guide them into place. This is especially helpful if you don't have long slender fingers.
The next step in this process is to determine what type of method is available for fixing the problem. You cannot just caulk a crack or fill it in with cement and hope for the best. Unfortunately, there is more work than this because you have to fix the problem from both the inside out and the outside in. This takes a professional in most cases to determine the best method for repair.
Investigate the plumber's reputation. Ask a neighbor before starting your search or check online for customer reviews. Call the Better Business Bureau or your city to ask about any complaints on file against this company. Finally, ask the plumbing company for references from customers. If they are reluctant to provide references water line repair call another plumber.
Keep your hands clean and dry. Plumbing jobs get slippery, so it's important to work with a pair of sturdy gloves so you don't lose your grip and accidentally hurt yourself or break something.
Plumbers can help keep small problems from becoming large problems. Do your homework before choosing a plumber and you can help to ensure that the job is done correctly and for a good competitive price.