Learn French: Le plombier va réparer la fuite d'eau. - The plumber is going to repair the water leak.

You would say Je vais faire réparer la fuite d'eau par le plombier. In our original sentence, the plumber is the main subject doing the action. To say you are having someone else do it, you use faire + the infinitive (réparer), and introduce the person actually doing the work with par (by).

Is the "b" in plombier pronounced?

No, the "b" in plombier is silent, just like in the English word "plumber"! It comes from the word plomb, meaning "lead" (the metal historically used for pipes), where the "b" is also silent.

Why is it fuite d'eau and not fuite de l'eau?

When a noun is used to describe the function, material, or type of another noun, French connects them with just de or d', dropping the article (le, la, l'). Here, d'eau acts like an adjective telling us exactly what kind of leak it is.

Could I use the simple future tense and say Le plombier réparera la fuite d'eau?

Yes, that is grammatically correct and means "The plumber will repair the water leak." However, the original sentence uses the near future (aller + infinitive), which is much more natural and common in spoken French for planned events that are happening soon.