Learn Dutch: Waarom ben je zweterig en zijn je ogen waterig? - Why are you sweaty and are your eyes watery?

They use the suffix -erig to turn a noun or verb into an adjective describing a tendency or physical state. Zweterig is formed by adding -erig to the noun zweet (sweat). Notice that zweet drops one e in the spelling to keep the vowel sound long in the new open syllable. For waterig, because the noun water already ends in -er, we only add -ig to achieve the exact same effect.

What is the difference between saying someone is zweterig versus zwetend?

Zwetend is the present participle (sweating), which describes the active, ongoing action. Zweterig, on the other hand, describes an overall state, tendency, or physical condition (sweaty or clammy). You can still feel zweterig even after you have finished zwetend.

Why is the word order inverted to zijn je ogen after the conjunction en?

The conjunction en links two clauses that are both governed by the question word Waarom (Why) at the very start of the sentence. The second clause is essentially asking "[Why] are your eyes watery?". Because it is a continuation of the same question, it requires inversion, placing the verb (zijn) before the subject (je ogen).

Could I use the suffix -achtig here, like zweetachtig, instead of -erig?