The Red Badge of Courage- Ch 18

I am confused about the beginning of this chapter. Henry is getting water for some of the other men, i think. When he was on his way back he heard other men talking about a battle that had started. Henry and Wilson were gonna go help another group and Henry's group was gonna just be there for back up. Everyone said that Henry's group is worthless and they should only be back up because otherwise they will all die.

• I thought that they just said Henry's group did good in the last battle because they made the enemy retreat. I don't understand why thay are saying they are bad?
• What was they water part all about?