AC voltage consists of a sine wave, it begins at zero volts, travels up to a peak value, then back down to zero, going on past zero to a negative peak value. The positive and negative peaks have the same magnitude.
110 volts is fed to an instrument via one "hot" wire with the above described waveform on it, and a neutral wire which is essentially ground.
220 volts is fed via two "hot" wires. Each consisting of 110 volts. However, when one wire's sine wave is at a positive peak, the other is, at that same instant, at a negative peak. So 220 volts is nothing but two 110 volt wires that carry waveforms which are 180 degrees out of phase with each other.
As an easier example, if you and your friend go into a building, and he stays on the ground floor, and you walk up ten steps to the second story, you guys are ten steps apart. But if he goes down ten steps into the basement, you guys are now 20 steps apart. This is the way that 220VAC works. It is two opposite phases of 110.
I said all that to say that 220 is rarely more dangerous than 110. If one "hot" wire becomes exposed to the water, it is only 110V; be it in a 110V system or a 220V system. The only rise in danger exists when a person touches both phases. That is, when he touches both hot wires. Then he has a difference of 220 volts across his body. That increases the danger. But my point is that 220V is rarely more dangerous to use in water than 110V. Because most shocks only occur by touching one point that you are not supposed to. Rarely will anyone simultaneously touch the two opposite phases.
Next topic, which is cheaper? Both cost about the same. If you purchase a motor which can be wired to run on 110V OR be wired to run on 220V, the question most people ask is, "Which is cheaper." The answer, "neither." Say you are connecting that motor to an air compressor. So for instance, you connect it to 110V, and it pulls, oh lets say 6 amps. The power company charges you for power. Power is equal to voltage multiplied by current. So your 110V times 6 amps equals 660 watts of power that the air compressor is pulling.
Now you take the same air compressor and re-wire it for 220V. When you turn it back on, it will pull 3 amps. Doing the math, 220 volts times 3 amps equals 660 watts. So the power company can not be cheated. If you are going to compress air with that compressor, it takes 660 watts of power to do the work, and they are going to charge you for 660 watts. Now, there is a savings in wire if you are running the wire to the compressor. Wire that carries only 3 amps can be smaller than wire that has to carry 6 amps. So you can save money in wire.
In either case, use a GFI for safety. Swampstalker, you mentioned feeling a shock in your water. You need a GFI and it will keep you from getting shocked. Although you have yet to suffer harm from the times that you got shocked, who knows about next time. Get a GFI!
