Meaning and usage of "as well as"
Yes, it means that there are 1000 words each for "water" and "louse", for a total of roughly 2000 words. Consider it this way:
There are roughly 1000 different words for “water,” as well as [1000 words] for “louse”.
The original version is simply a shortcut.
By the way, in math, this would be the distributive property:
1000 words (water + louse) = 1000 words (water) + 1000 words (louse)
When someone says "as well as" it generally means "and in addition," which is the same thing as saying "and." Thus, "as well as for louse" is the same as saying "and for louse." See Merriam-Webster's definition.