Learn Turkish: Su pek soğuk değil. - The water is not very cold.

In Turkish, while çok means 'very' or 'a lot', you generally use pek when making a negative sentence. The combination of pek and değil means 'not very'. If you wanted to say the water IS very cold, you would use çok and say Su çok soğuk.

Is there a word for 'is' in this sentence?

No, there isn't! In Turkish, you do not need a word for 'is' or 'are' when describing something with an adjective. Just placing the subject su (water) before the description pek soğuk değil (not very cold) automatically means 'The water is not very cold.'

Does the word değil follow vowel harmony rules?

No, değil is a standalone word meaning 'not', so it does not change its vowels to match the word before it. Even though soğuk ends in a hard back vowel (u), değil stays exactly the same.

Can I use pek in a positive sentence like 'Su pek soğuk'?

Usually, no. The word pek is almost exclusively used in negative sentences or with negative meanings. For positive descriptions, you should stick to çok.