They are called 部首. And, in antique dictionaries like 康熙字典, they are referred to as 部. It is very formal and scholarly to address the whole bunch of characters containing 氵 or 水(at the bottom) or other parts showing links to 水 as 水部. The logic here is ''the original character of the radical' + 部', following the rules of classical Chinese.
However, in everyday life, when we describe how to write an unfamiliar character or admiring calligraphy, we cannot address both 氵 and 水 as 水, because they are too vague for radicals in different positions. Popular names are called for, and here I enclose a list of popular name for radicals found on wikipedia.
Popular Names for Radicals(Chinese)
三点helps you visualize the radical.字旁means the radical's position is at the side.字头means it is at the top. – 杨以轩 Jan 12 '14 at 03:07