I'm glad it wasn't a worse electrocution. To get that kind of a jolt so serious that it split open the flesh, I would assume another part of the body was grounded when the hand touched the water. 

It's important to remember that we are working with electrical power that, under the right conditions, can actually kill us. Proper precautions are vital to our safety.

Because our electrical powered devices are underwater, the plastic insulation on the device and it's power cord is our only protection from electrocution. That insulation must have a perfect seal where it enters the device housing. We must be vigilant to check devices for cracks and power cords for kinks, bends and actual cracks in the insulation. The most common place for a power cord to crack and fail is next to the pump itself. To ensure the insulation remains intact to do it's job:

- never lift/carry a pump or any electrical device by the cord. 

- never wrap the cord tightly so that it makes a sharp bend at the point where it comes out of the device. I commonly see this on heaters and pumps stored and for sale. Not good. 

- never pull a cord to unplug it from the outlet, always grasp the plug itself and if the plug feels overly hot, replace it. It has become compromised.

- never use a device so old that the insulation has become stiff and brittle.

- never use wet hands while working on electrical and never stand barefoot on a cement floor or wet floor.

- never set up any electrical connection so that accidental water can drip/flow into the connection. Instead, do attach power strips and Apex power bars upside down or sideways to a solid surface (roof or wall of aquarium stand) away from the path of accidental water flow. This way the off switch can be immediately pushed and/or plugs can be pulled out with one hand. This simple improvement can prevent a house fire. 

By trying to practice electrical common sense I can recall having had only one incident in 24 years of working on close to 1000 individual tanks. 

Here are two instances where electrical common sense was lacking.

The previous owners of a used Laptop Computer had unintentionally left a kink in the power cord. The kink had been pulled so tight and left for so long that when the kink was untied, the cord has become hardened in a permanent curl. The laptop is now mine and I'm concerned and being careful not to pull on the cord too hard to straighten it. This might make the insulation crack or break the wires inside the insulation.

An old black box aquarium LED fixture had evidently been housed for some time in a closed hood in constant overheating. The insulation on the power supply cords became slightly hard and brittle. One of the power cords had been kinked so hard at the plug to the fixture that the brittle inner insulation had cracked, allowing the 2 wires to touch and short circuit.