You have a lot of company. Many of us have done stupid things that have caused the death of baby chicks. It's unfortunate that these fragile creatures pay for our learning curve.
Chicks will find an open dish of water, fall into it, flounder, and drown. For that reason, there are water bottles with very narrow and shallow water basins. If you have to use a dish for water or if you need to put a dish of water for humidity where a chick can get to it, placing small rocks or marbles in the water will prevent a chick from drowning in it.
When you have baby chicks, you need to try and make things as chick proof as possible since the little twerps are so good at finding ways to kill themselves.