Why should I never shoot at water or hard flat surfaces?

Water, concrete, asphalt, flat steel, and hard wood reflect projectiles at unpredictable angles with surprising retained energy.

Water in particular looks soft but acts hard at airgun velocities; pellets routinely skip across ponds and travel hundreds of yards. Steel targets need to be angled to deflect pellets downward into a safe area, never face-on, and require minimum standoff distances (often 10 yards minimum, more for high-power guns).