>>17538666in french, as i'm sure you've noticed, many nouns are given the words "le" [masculine/neutral] and "la" [feminine], which mean "the" in front of them. it's more or less simply how the language is constructed. l'eau is what you saw - in french, the redundant "e" would be removed [water is masculine] and replaced with that apostrophe. if that didn't happen, it would be le eau. you must've forgotten about the apostrophe or figured it didn't matter.
it's a little hard to explain when you do and when you don't add it, but for example "je veux de l'eau" would mean "i want some water" whereas "eau" would be more like a... general term for the word, i guess? for a name it wouldn't include the "le," though. people who are named "ciel" or "sky" aren't called "le ciel" because then it sounds like you're talking about the actual sky.
and it doesn't sound like "lou" when pronounced, it sounds like "low."
tonnerre is actually "thunderbolt,"btw, right down to being used as the french name for the move thunderbolt. "eclair" is actually lightning, but can also mean flamboyancy, kinda like "flaming" in english.
