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Comment by viraptor | Hacker News Reader

I have to admit, I know very little about city-wide water systems, but since they cannot be realistically based on gravity there have to be pumps that add the pressure to the pipes providing drinking water. Doesn't that just mean they're making water companies spend more electricity to pump the water and get back tiny bits at customer's site?

The flushing part seems more interesting, but apart from single homes doesn't that have the same effect as partially blocking the toilets? I know that too much pressure difference in apartment buildings can have very bad results...

So does it really make sense, or is it just "stealing" the power from water company?

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From what I read on reddit some time ago when this was posted. With completely false number.

In our example city, you need to pump water on high ground, and then let it flow down. The high ground is at 30 unit. The water will be at the right pressure between 30 and 20.

But when it will reach 20 and below, there is too much pressure for the pipes! What is currently used is some kind of pressure relieving system that will release a bit of the pressure. The water can now come down between 20 and 10.

But then again, there's too much pressure for the water to go from 10 to 0 without damaging the pipes. Another valve is there to take care of this.

So, for now, energy is used to pump the water up, and then we have to waste that energy when the water goes down in order to maintain acceptable pressure. With the new system, a part of the energy that was used can be harvested again.

This is the same idea behind harvesting the braking energy on hybrid cars.

Makes a lot of sense, thank you!

I'm not an expert but my intuitive understanding would be that you are recapturing some of the energy required to pump water to households in those area in which gravity does some work to allow water flow.

From my experience with drip irrigation it surprises me that this generates enough electricity to be worthwhile, since you need tremendous height to get any amount of pressure in a gravity fed drip system, and that is still much lower pressure than typically flows into a home. Article isnt clear on how much is saved...

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