The plumbing courses cover all the aspects that you will be required to deal with as a drain line repair. You will be taught about the basic aspects as well as about health and safety issues and sanitation.
It water line repair is advisable to speak to neighbors and friends regarding the same. If any of your neighbors or friends has had a plumbing emergency and has been happy with the plumber they engaged then it is best to contact the same plumber. Family may also be of some help as far as recommendation is concerned but neighbors are a better option because they will give you details of an agency in the same area as you.
Another obvious indicator is if the water you get is close to cold as ice, then your water heating device has already reached its maximum level of service. If it can talk, it might have been shouting at the top of its voice telling you it needs replacement.
OR, you can think about developing a group, where relationships prevail, your time and efforts come with great rewards, and you can multiply your efforts through helping others succeed, as they help you with introductions and referrals. So with much less time and effort, you can benefit from creating your own referral group.
As with anything, when you are not sure how to fix a plumbing issue and when you don't have the proper equipment, you should contact a professional. They can usually find out what the problem is and resolve it for you in a short period of time. They will also be able to tell you if you have any other problems and water line repair they can suggest resolutions.
When doing the install on a water heater, keep an eye out for unconnected pipes. A commonly missed pipe is the one that leads out from the area for drainage. It is probably a recirculation pipe; that helps your water remain heated without wasting too much water.
Sometimes there can be complications of broken toilet flanges, closet bolts or rotted sub-flooring. If you find any of that in your situation, it will need to be repaired before reinstalling the toilet.