There are other skills plumbers need aside from being able to work with water. One of the most common things that a emergency service on is fixing water lines.
When you get to the house stand if front of the toilet and locate the water shut off valve. Should be down below the toilet on the wall. Just turn it off (righty-tighty) completely and flush the toilet. All the water should have left the tank, well at least most of it. If there is remaining water line repair get it out with paper towels or a rag. The important thing is that no more water came in. If it did then your valve is not shut all the way or not working and you need additional help.
Leaks can occur anywhere in your reverse osmosis water filter system. If this ever occurs, check the source of the leak. It may be from the hoses, fittings and the valves. Most of the time, some kind of tightening might be necessary. So make sure to securely tighten the fittings. If this does not work, you may need to replace the filter itself, however that might take a bit more work.
Depending on your repair job you might need a bucket that will fit below the sink trap, as well as some rags and newspaper. Masking tape is useful for labeling and for wrapping around the heads of the wrench to protect your chrome tap handles. Rubber gloves are recommended, particularly when working with the toilet, but there are greases and glues that you may not want on your hands.
Here are some general cautions. Do not begin jobs on holidays, weekends, or at times when plumbers raise their rates or are difficult to reach. Do start early leaving plenty of daylight to call a plumber if something goes wrong. Study the situation carefully. Think about what might happen if something suddenly broke and what the effects would be. Old corroded copper tubing might break in the wall when you are wrenching an angle stop that supplies the water line repair to your toilet. A flood in the wall could be costly. If the angle stop, on the other hand, is new and shuts off easily and you have another toilet in the house then it might make sense to repair the toilet yourself. Be honest, too. Are you handy with tools? Did you do well in shop classes in school?
Turn the water off at the main shutoff valve at the street. You should be able to take a pair of pliers(or your bare hands) and turn the valve at the water meter to shut off the water to your home. Once you have shut off the water you can cut the pipe around the leak and make the repair.
Find out if the plumber works on a 24 hour basis and, if so, what are the extra charges involved. More important than the costs however are the person's trustworthiness and reputation. After all, he or she will be in your home and around your possessions. You should feel comfortable with their presence and confident that they are honest.