For instance, how would I translate the following sentence?
Where is my water?
And I mean specifically using eau, not cheating by using mon verre. Would it be Où est mon eau? or Où est mon d'eau?
Où est mon eau?
Would be the correct translation here.
You seem to have trouble with d' here. Let me clarify:
Mon verre d'eau ~= Mon verre de eau as in Mon verre de lait
This is the actual way to read it, but you always contract the de if you can. It's the same as My glass of water. In English you wouldn't say Where is my of water, right?