Polish verbs in 99% of the time don't show any difference between Present Simple and Present Continuous. "Tygrys teraz pije wodę" adds an additional word "The tiger is drinking water now". And even this could be translated to "The tiger drinks water now" as well, I believe. Like, he used to only drink coffee but then he decided that maybe he should drink water instead so nowadays, his only drink is water ;)
Anyway, the sentence is even closer to Present Continuous than Present Simple. There's a habitual verb "pijać" (Tygrys pija wodę) which would make it obvious that Present Simple is needed, so actually Present Continuous is more probable. Although the habitual verbs are out of the scope of this course as the 'normal' verbs are enough.
Well, the basic verb is "pić", but it also has a 'habitual' equivalen, which is "pijać".
"pić" can be translated either into Present Simple or Present Continuous, "pijać" can only be Present Continuous.
You don't have to know it, you don't have to use it, "pić" is enough, at least until your Polish gets more advanced.