You must log in or register to comment.

JohnnyJordaan t1_jdsi8n1 wrote

They are local pumps in various part of the system to ensure the local pressure is high enough to reach around 6 stories high while then still having enough pressure coming out the tap on the top floor. Buildings that are larger than that needs to use their own pump to pressurise it further to reach the higher floors. They often combine it with a water storage tank on the roof, to not require huge pumps to meet demand when everyone is taking a shower at the same time.


Imhumanator t1_jduastc wrote

Would this mean lower floors could potentially have higher pressure I’m the < 6 story scenario?


JohnnyJordaan t1_jdulje6 wrote

In a large building the pressure would generally be higher in the lower floors as there’s more water ‘leaning’ on it from all the floors above it. However as there are safety regulations for the maximum pressure at any point in the system, they often use pressure valves to make sure it will not rise above a certain pressure (eg 75 psi). So that way you generally won’t notice a difference between the floors in a building. In a small building without pressure valves it’s true that the lower floors will have the highest pressure.


fiendishrabbit t1_jdunnkg wrote

The potential is there, but there are water pressure regulators installed that lowers the pressure in the tap to where it's supposed to be.


fiendishrabbit t1_jdunefw wrote

There are a lot better reasons for a water storage tank on the roof than "to not require huge pumps to meet demand when everyone is taking a shower at the same time".

Pumping into a tank means that the pump does not experience any water hammer effects (which can ruin the pump) and it means that water pressure from the tap is even (since the pressure is determined by the height difference between the water surface and the tap) rather than fluctuating as it would if it was actively pressurized by a pump.


JohnnyJordaan t1_jdupfmm wrote

Those are indeed important advantages but not strict requirements for the system to function, I meant it in that regard.


BeneficialWarrant t1_jdsk5c1 wrote

One of the nice things about a water tower is that the pressure is not really affected by flow rate (unlike a traditional pump which has a limited power output and where the pressure drops off as flow rate increases).

Potential energy is stored in the tower. If more people turn on the tap, the potential energy just gets used faster. So long as the tank doesn't run dry, there will always be water pressure for everyone. Then a pump can slowly supply the tower during times of low use such as nighttime.


Geotolkien t1_jdsm3v3 wrote

Municipal water systems and water companies generally provide enough pressure from pumps and / or water stored at higher elevation or in an air pressurized storage tanks.

Taller buildings have to have their own pumps and occasionally tanks to lift and pressurize at higher elevations.

Water systems with extensive change of elevation typically have pressure reducing valves that isolate higher elevations from the lower elevation portions of the system so that the force of gravity doesn't overpressurize lower elevations and rupture pipes, and also have valves so that leaks in lower elevations don't dewater higher elevations, creating such an aggressive siphon as to implode water heaters and other tanks at higher elevations.


KingdaToro t1_jdss9ja wrote

This is what water towers are for. When you have a roughly 160 ft tall column of water, the water at the top will be pressing down on the water at the bottom with the right pressure for homes and apartments to use. Pumps are used to fill the water towers.


MidnightAdventurer t1_jdsmo2o wrote

Most urban water supplies use reservoirs of water high up so that gravity does the work of keeping the water moving. At that point, all you need is big enough pipes that the flow rate doesn't slow the water down enough to cause problems. Too much flow in too small a pipe increases the speed and thus the resistance to flow reducing the pressure at the other end (pressure is only constant at the same level when the water isn't moving). These supply pipes can be over a meter in diameter, sometimes even larger. The size steps up, the more properties are supplied be the pips - where I am its generally 15-25mm for a single house, 100mm along most streets, 300mm feeding multiple streets etc. A recent project in my city was a 3m diameter pipe from the reservoir in the hills outside the city

Depending on the terrain around the city, the main storage areas might be too low for this to work properly, in which case, you can use pumps or water towers resupplied with pumps. Particularly tall buildings may need to use pumps or their own tanks in the top of the building to ensure the pressure is maintained as they may be higher than the main reservoirs or close enough to reduce the pressure below the required level.


[deleted] t1_jdstjaf wrote



Phage0070 t1_jdt0l21 wrote

Your submission has been removed for the following reason(s):

Top level comments (i.e. comments that are direct replies to the main thread) are reserved for explanations to the OP or follow up on topic questions.

Links without an explanation or summary are not allowed. ELI5 is supposed to be a subreddit where content is generated, rather than just a load of links to external content. A top level reply should form a complete explanation in itself; please feel free to include links by way of additional content, but they should not be the only thing in your comment.

If you would like this removal reviewed, please read the detailed rules first. **If you believe it was removed erroneously, explain why using this form and we will review your submission.


buildyourown t1_jdtkpsu wrote

You ever see those big water towers? That height difference provides the water pressure


chunkoco t1_jdu546a wrote

Water is stored in a higher elevation than the city. This water column has a lot of weight (water is heavy) this pressure differential translates into running water to anything located under the water column.


[deleted] t1_jdsgwmu wrote



Maxweilla OP t1_jdshsp9 wrote

With buildings id understand pumps, but each house has one too? Cool thanks


Careless-Ordinary126 t1_jdsjd29 wrote

They dont, there Are Water towers or tank on high enough place, you pump Water there And the Water just naturaly flow down to your house


travelinmatt76 t1_jdt6wgr wrote

For questions like this you can check out Pratical Engineering on YouTube. He has all kinds of videos on pipes and waterways and nice demonstrations on how everything works. Here's his video on water towers.