When I turn on the faucet or shower, water, presumably from a main buried in the street, flows out freely. Clearly the water must be under pressure, or it’s magic and can defy gravity.
So where does the pressure come from? There are no pumps between the main and my house as far as I know.
Water towers. Great big tanks of water up on stilts. Pumps run all day to push water up into them, and when you open the faucet water flows downhill through the pipes and out of the tap.
Yeah that all makes sense. But I feel like in order to supply enough water to everyone in an urban area like where I live, there’d have to be water towers everywhere, yet I rarely see them.
Anyway, thanks for the quick responses.
You may be confusing quantity with pressure. A tall tank is necessary to provide pressure, but it doesn’t have to be big to provide quantity, as the water may be pumped up just before use.
There are other ways of providing pressure than gravity flow. I have a private well, and the pump pushes water into a small (20 gal?) tank with a rubber bladder. When the bladder fills enough and the pressure increases to about 50psi, the pump shuts off. As the water is used, the pressure drops, and when it gets down to 30psi, the pump turns on again.
This tank is in the basement. If I had a 2 story house, the pressure settings would have to be adjusted upwards just a bit.
Before the bladder tank was installed, I had a similar tank with an internal air space at the top which provided the pressure. The only problem there was the air would sometimes leak out and the air pocket had to be re-established.
I never really noticed them in my area growing up because we had hills and trees. They were just up some unassuming dirt road with a few county signs posted and maybe a fence, and they were just a large tank instead of the tower you usually think of. They are a lot more noticeable in flat areas with little to no trees like farming towns in the Midwest.
Where do you live? I think most of Detroit’s water, for example, isn’t pressurized by water towers at all, but by pumps. I tried looking for a cite, but couldn’t find one quickly.
I live in Ann Arbor, and our water system does use water towers. I know where a couple are off hand, and Ann Arbor water isn’t that big compared to Detroit’s. If you don’t know where any are around you, maybe they don’t use towers.
Thanks Musicat, you cleared it up for me.
ZenBeam - I live in Oakland CA. Where I live it’s flat, but there are hills nearby. I can think of only 1 tower in the whole area (with ~300K inhabitants), so there must be others hidden up in the hills.
Pump stations are small and easily overlooked. Ours often look like little sheds attached to Fire Stations*. If you have enough hills, it may be as **sitchensis **discribes. If you’re in a flat area and you don’t see any towers, then it’s pumps.
*Because, hey, the City already owns the lot.
I work for a water utility. Most of our water comes from reservoirs miles away that are at a higher elevation than our service area. The water flows downhill by gravity, through the treatment plants, and into the mains, with no pumps required.
In some higher elevation regions of our service area, however, we have to pump the water to maintain a high enough pressure. These areas also have water towers.
Pumps and water towers work hand-in-hand. Without water towers, the pumps would have to operate continuously, even during low-demand periods. With water towers, the pumps pump water up into the towers, which then maintain pressure. As water is consumed, the level in the water tower drops until it reaches a certain point, which actuates a level switch to start up the pumps again.
You can’t have water towers without pumps. You can have pumps without water towers, but would always need to keep the pumps running (which is not generally practical).
Here’s a (pdf) map of the water system that serves Oakland. Note that there are indeed several reservoirs in the hills north and east of the city (towers not needed there - the hills are plenty high).
True - there’s one in River Forrest IL that looks like a very nice house. I suppose this was a necessity because it’s on a normal lot in an expensive area.
The water company has pumps at the water source. The pumps maintain the pressure on the system. Today speed drives control the speed of the pumps. As demand goes up the pumps speed up. Depending on the city the system pressure can run from 50 to 120 PSI. In my neighbor hood the main is 60 to 80 psi. At that pressure no pump is needed to get the water into the house.
I thought it was the other way around, kind of. If all your pressure comes from pumps, you need to have enough to meet the peak demand (when everybody is taking their morning shower, I would think) and then most of them sit idle the rest of the day. With a tower, the pump is sized for average demand; the level in the tank drops during peak demand and then it gradually refills.
I’ve also heard you don’t want the water sitting too long in the tank. After it’s been treated, you want the water used quickly before the treatment chemicals wear off and bacteria have a chance to start growing again.
The water in NYC comes from the Catskills and I believe that all its pressure comes from gravity flow.
In Norway the water pressure is nearly always from the reservoirs being at a higher elevation than the consumer. In fact the equipment downstream, so to speak, from the treatment plant is more likely to exist to decrease pressure rather than increasing it.
Yes, I know, which is why I found it surprising that Detroit doesn’t use water towers for the most part. I tried last night to find a cite, and I’ll try again tonight.
I don’t believe any of those are municipal residential water supply towers. Five are factory water towers (although #4 is iffy), one is the Detroit Zoo water tower, which is not operational. The last I’m not sure of, but that picture, frankly, looks so old I’d question whether the tower even still exists. I’d also question whether any of those are still in use.
The water need not be stpored in a tower if there are hills nearby. Many times a municipality will store water in a cylindrical tank up on a hill instead of building a separate free-standing tower.
These towers or tanks, by the way, contain the treated water ready for use. Reservoirs may contain water at a higher elevation, but before people can use it, it must be filtered in stages and any additives put it (water companies will often add a small amount of water softener, even if you don’t have anything like fluoridation). Since it takes pressure to send the water through such treatment facilities, I suspect that natural water pressure from reservoirs at any height is used for this, and that drinking water is generally pumped into elevated and enclosed storage chambers like stilted water towers or tanks on high elevations before home use.
You could try the Detroit Water and Sewage Department site for further information; the master plan is quite detailed. On this page it states that they do use elevated storage towers and why they are required to do so but from reading thru the master plan page they don’t do a lot of elevated storage. Still, they do have some rather large pumps listed.
