Rapid decomposition requires optimum water content. If the compost pile is too dry, bacterial activity will slow or cease. If the pile is too wet, loss of air in the pile will lead to anaerobic conditions.
Optimum Water Content
Ideally, pile water content should be at 40-60% (as wet as a squeezed out sponge).
If your pile is too dry, add water as you turn the pile.
If your pile is too wet, add browns and/or turn the pile.