"He is drinking good water."
Translation:Li trinkas bonan akvon.
You'll have to post the whole sentence; it's possible that the problem was not with estas but with something else in your sentence.
- Li estas trinki akvon. = He is drink water. Wrong in both languages.
- Li estas trinkas akvon. = He is drinks water. Also wrong in both languages.
- Li estas trinkanta akvon. = He is drinking water. Possible in both languages, but less common in Esperanto than in English.
Yes to the first sentence, "He is drinking good water" could be Li estas trinkanta bonan akvon but is more commonly said in the simple present tense, Li trinkas bonan akvon.
Li estas trinkas bonan akvon makes no sense in Esperanto, just as little as "He is drinks good water" would in English.
The past tense would be Li trinkis bonan akvon for "He drank good water", and if you wanted to be specific about a continuing action you could say Li estis trinkanta bonan akvon for "He was drinking good water".