Work is also power so you can't reuse power because it's already gone into the work that it's done. Eventually all power becomes heat and you can only claim work from heat if you have a cold sink. There's less energy after work has been done, the water isn't moving enough to generate the power required to move it in the first place. What you're suggesting is eating your cake and having it too. Another analogy is if I gave you 50 cents for every dollar that you gave me then by your reasoning, you could be a millionaire just by giving me enough money, after all they do add up. All the sources still add up to less than what it was originally.

> Take the water in your house,

>I realise you couldn't get it all back but if you could retrieve frations of energy from multiple sourses from every household, wouldn't that add up?

The problem is that the amount of energy available in the water system is miniscule. So small that I doubt if anyone has bothered to calculate it.

For example you might pay the electric company $0.10 per kWH. The cost of equipment/maintenance to extract and utilize the power available from the water flow might be $1000 or $10000 per kWH. It really doesn't matter which.

As for the general idea of "recycling power", it sort of depends on how you define ""recycling power".

Examples:

1.

It's fairly common to use the waste heat generated when producing electricity for things like preheating water to reduce fuel consumption or process heat/heating buildings.

2.

Air to air heat exchanges can be used to salvage heat. For example in a cold climate the heat in exhaust from a building can be used to pre-heat the incoming fresh air; reducing the amount of fuel needed to heat the building. The same idea is sometimes used in industrial heating processes where exhaust gas is used to heat brickwork, and then the flow is reversed to preheat air which reduces the amount of fuel needed.

It all comes down to return on investment. If you can spend $1 to save $2, that's good. If it costs you $2 to save $1, that's bad.

3.

If you want to stretch the concept, you could say that a hydro electric dam "recycles power". The power originates to solar energy from the sun. In the absence of the hydro electric dam mother nature would just convert that energy to heating the water & air. The hydro electric dam "recycles" some of that energy and converts it to electricity.

Using water pressure wouldn't help since that water pressure has to come from somewhere- the water company. They'd just charge more for water if you did that plus you'd be wasting lots of water. Heat is the best thing to recover that is wasted in most houses. Got a bathtub full of hot water? Let it sit for half an hour or so after you're done and the heat will escape into the room. Same can be done for washing machines and dishwashers but it would take more work. Very tight houses that don't leak air reclaim heat from exhaust fans before pumping the moist air outside.

The reason is that conversion of energy is rather imperfect because of the laws of physics. For the water to run in your home, energy is expended. You could only get a fraction of that energy back if you used it to generate electricity. So, on the whole, it's more efficient to get the energy directly.

For example, straight from the one sustainable source: the sun.

I am no where near an educated man in the ways of electricity. But, it would seem to me that one could use plenty of things around the home to recycle power. Take the water in your house, power companies regularly use moving water to generate electricity. Why doesn't turning on running water in your home do the same?