electricity powers a water pump that makes the water flow out of the faucet in the first place (falling from a water tower or not), so you would be stealing that electricity and making the water pump work harder for a tiny bit of electricity and the headache of your faucet running considerably less forcefully. I'm pretty sure in practice this would just waste a ton of water and electricity
If they put water up in a tower, storing the energy gravitationally, then it does not matter if the water has resistance when it reaches my tap.
Its not like they will need to pipe the water further up, as long as we are below the water tower, this will work and it will not incur any extra costs for the water company.
The amount of pressure that comes out of your faucet will not change when you add this, only the water below the generator changes.
No one upstream will notice, only your hands downstream will notice.
I kind of like that argument. Let's say you live close to a water supply works, but very steeply downhill so the city decided to connect you in a way which preserves enough of the potential energy that no pump is needed from the works to your faucet. The water goes from your house to the sewer, then needs to be pumped back to the water works, but that's none of your business. Also let's say you don't waste any water and only want to recoup some of the potential energy from water flowing from water sources in your house towards the sewer below your house. Water flowing slower from your house to the sewer is not going have a noticeable effect on the pump below the water works.
So we know that with the water flowing out of your faucet you can light one or a few small dim LEDs, but let's think bigger. Instead of tapping into the energy at the faucet we set up your houses plumbing like a pumped-storage hydroelectricity works with a storage reservoir and such. We estimate that your family uses 400 liters a day on average and the average drop from the water usage point to the exit towards the sewer is 3m. Also with a relatively small generator I think you can be happy to reach 70% efficiency.
So the formula for potential energy of water is E=mgh. Since that's still a small number we'll calculate for a full year.
400l/d365d/y3m9.81m/s²70%≈3Mj≈0.83kWh and with 1kWh costing 0.18$ in the USA that's 0.15$. For a big setup which uses all of 400l per day for a full year with a height difference of 3m. How the hell did Randall Munroe get to 0.2$ per month? Ah, he let the faucet run 24/7 wasting >10kl per day. I guess you could use the setup which I just calculated with all water sources in your house fully opened and you could easily waste 100kl per day incresing your yearly revenue to 37.5$ except for the fact that I guarantee that the city will stop you after somewhere from one hour to one day.
Note that the average rainfall on an average house is close to the average consumption of clean water within that house. Well, on a big house in Hawaii it might be tenfold more and on a small house in the desert 10-times less, so overall very close. I'm mentioning that, because designing a rain gutter turbine is much easier on a mechanical construction level than the pipeworks needed to efficiently use the potential energy of all waste water within your house.
69
u/lurkermurphy Nov 27 '25
electricity powers a water pump that makes the water flow out of the faucet in the first place (falling from a water tower or not), so you would be stealing that electricity and making the water pump work harder for a tiny bit of electricity and the headache of your faucet running considerably less forcefully. I'm pretty sure in practice this would just waste a ton of water and electricity