The first thing you need to keep in mind is the company that you will hire for the work is a plumber. Plumbers are usually licensed and have passed their examination. So, when you get a call from someone, you can immediately ask him or her to make a test on the water supply coming into your house.
Next thing you need to keep in mind is the expertise of the plumber. Before hiring any plumber, make sure that the company has been established for quite sometime and has experience in their work. There are lots of companies that are not well established and have hardly any experience in their work, hence you should make sure that the company is certified by a recognised body.
After finding out the company you want to hire, the next thing you need to do is to visit them personally and speak to them. You can also ask them about their expertise and credentials. Make sure that the company can give you the information you need on the work they are doing.
Remember, the best way to find a plumber is to ask for it. You can do a simple research online and you will be able to get an idea on what is the expertise of the company.