The trenches often flooded and it took long periods of time for the water to drain.
Oh no, the trench has been flooded for 6 days!
The water was dirty and carried disease. The soldiers spent long perionds of time soaked in them so some of them developed a hideous disease called Trench foot. It inflamated the feet and made them supurate, it was really painful.
Ahhh, I have trench foot!
Sometimes the disease was so strong and damaging soldiers needed to be carride outside the trenches or the dressing room to the field hospital for treating.