Durante la pausa pranzo mangio un panino e bevo acqua fresca.

durante is a preposition meaning “during.” You use it to introduce a period of time or an event. In this sentence, durante la pausa pranzo means “during the lunch break.” Form:

• durante + [definite article] + [time/event noun]
  Examples:
• durante la lezione (“during the lesson”)
• durante l’estate (“during the summer”)

In Italian, pausa pranzo is a common compound expression for “lunch break.” Although pausa del pranzo isn’t ungrammatical, it’s less idiomatic. Native speakers drop del when two nouns form a fixed concept:

• pausa pranzo (“lunch break”)
• vacanza studio (“study holiday”)

Italian is a “pro-drop” language: verb endings carry person and number information, so the pronoun is often unnecessary.

• Mangio un panino already implies “I eat a sandwich.”
  You’d include io only for emphasis or contrast (“Io mangio, tu lavori”).

In Italian:

• fresco often means “pleasantly cool/fresh,” especially for drinks and produce.
• freddo means “cold,” possibly too cold or even freezing.
  So acqua fresca suggests a pleasantly chilled drink, whereas acqua fredda might feel almost icy.

Yes. Italian word order is fairly flexible for adverbial/time phrases. Both are correct:

• Durante la pausa pranzo mangio un panino e bevo acqua fresca.
• Mangio un panino e bevo acqua fresca durante la pausa pranzo.
  Moving it can slightly shift the emphasis, but the meaning stays the same.

Yes, but there’s a nuance:

• durante il pranzo refers to the meal itself (“while I’m eating lunch”).
• durante la pausa pranzo highlights the break period (often implying you’re at work or school). Choose based on whether you mean the act of eating or the break around lunchtime.