Likewise, a woofer (you) will only draw as much power (water) from an amp (the well) as needed in order to acheive the desired volume (quench your thirst).
The water analogy works well for describing electricity, but the way you've presented it here paints the wrong picture. Speakers do not draw anything, they are more of a flow restriction than anything else.
I've been meaning to write this up for a while. Consider this my first draft.
As I said the water analogy works well. So lets assign some common water works parts to an amplification/speaker system.
The electric grid is like a reservoir feeding a large area.
The power supply in an amp is like the a water tower covering a community.
The capacitors would be like a pump in a house.
The output transistors are a valve.
The speaker is plumbing after the valve.
We'll ignore the voltage/current thing for now, and I'll say power. But if you want to think about them, in terms of water, voltage is how much water there is, and current is how much pressure is behind it. You can have a lot of water at low pressure, and it'll just flow calmly, like a sewer pipe. Or you can have a little water at very high pressure, and it can be used for cutting, like a water saw.
The electric grid has a pretty much unlimited supply of power from the point of view of the amp. But only part of that is being made available by the power supply. You can't draw any more than power supply makes available at any given time. But if you need a little extra push for a short period of time, you can rely on the capacitors.
Most multi-channel amps have one power supply, and one bank of capacitors for all the output transistors. Think of the output transistors as a number of push-button valves. They're all fed from the same source, if you open all of them at once you'll come closer to exhausting the supply. But even wide open they can only flow so much. The reason I said push-button valves is because of what they're doing. Think of a valve that automatically springs shut when you stop pressing on it. But the harder you press the more water that flows at the time. The pre-amp stage is what's pressing that valve open. It's taking a little action, the desired output waveform, and causing it to be amplified by opening and closing the valve in the same pattern.
Finally after the valves there are a series of pipes. If a speaker has high resistance those pipes are narrow. If it's of lower resistance then the pipes are bigger. If you connect two pipes in parallel they'll have half the resistance of a single pipe.
Here's where the analogy breaks down. Water vales don't suffer the same was transistors do when they're turned wide open, and have big fat pipes behind them. But if you can imagine the water being damaging to the valve, and the valve itself not being designed to flow into an open space, but only being spec'd to use a specific diameter of pipe or smaller you can get a better idea of what happens with a too low of resistance speaker.
As I said, first draft, just off the top of my head.
