This thought occurred to me while driving through Cherry Hill NJ last night by one of their two water towers. I then saw one by Camden while going over the Ben Franklin Bridge, and wondered what they are for. I can’t imagine it is for emergency drinking water, as there are way to many people living in these communities.
So, I know they hold water, but for what? Are they used for fire emergencies, for emergency water in case of some disaster, or something else.
They provide stable constant water pressure to things: your own municipal water supply probably has a tower or two. By putting a large volume of water on top of a tall skinny pipe, you have the umpteen feet of water pressure being held fairly constantly as long as the tank never drains enough that the level drops into the neck.
As demand rises and falls, the tank will smooth out the ripples, with a pump filling it up at a slow regular pace while people are drawing out water at different rates.
The pressure needed to supply a community with water during peak hours is too great for the city’s pump. By continuously filling a watertower with the pumps all night and day, the pressure the water tower uses (gravity) can fill the need during peak hours.
The two above me nailed it, but water towers are also a reservoir for fire emergencies, like you guessed. My two pumps supplying my tower each can put out about 1200 gallons per minute, but a fire can go through water faster than that. So we have half a million gallons sitting around waiting to be used too.
With a more modern system (that we’re getting later in the year) we would use the pumps to fill the tower in the off-peak hours when the electricity is cheaper too. For now, one is on manual control and the other turns on when the pressure in the lines drops below a certain point, indicating that the level in the tower has dropped.
Jules - Drinking Water Operator (among other things)
Also, if for some reason the pumps fail (Power outage? Fire? Alien attack?) you still have water pressure, at least for a little while, and perhaps long enough to get the situation fixed.
Moving thread from IMHO to General Questions.
Why are so many water tanks elevated several stories high on stilts? I would think you could get the same result at less cost with a tank that is closer to the ground.
The higher they are the more pressure they provide. There must be regulations on minimum water pressure. I’m guessing in the area of 50 psi; that would equal about 110 feet of water.
Back to the idea of constant pressure. Every 34 feet of water gives you 1 atmosphere of pressure (14.7 psi). If you make it tall enough, you can maintain enough pressure to get the water to flow to upper floors of houses and the like without extra pumps in everybody’s homes.
Sure, the water system pump has to do the work to get the water up there, but as long as the water is not being consumed in great amounts, the pressure will always be present in the system as long as there’s water in the tank.
The simplest and best explanation (that I heard here), is that it allows you to use pumps sized for the average local water useage, rather than for maximum local water useage (which would be significantly higher).
This is another of our more popular areas of inquiry:
Water Towers 12-26-2000 (Question is about water freezing in them, but there are links to general descriptions)
someone explain how a private well works 04-25-2002 (Mentions towers only in passing, but provides some interesting information)
Water Towers 03-12-2003
Another civil engineer Q regarding water towers. 03-25-2004 (Not directly relevant, but it does provide a few more facts)
The master has also provided a (somewhat cryptic) comment:
Why are water towers are elevated, while petroleum tanks are on the ground?
'We don’t have water towers where I’m currently living. It’s all pump fed. And the pumps are addressable. And there’s a drought so our municipal pumps are only addressed to provide water for four hours per day!
Here’s how this works. Everyone has a cistern. They’re commercially produced, and common sizes are 450 liters, 1000 liters, and 1500 liters. They’re black, which is just perfect for heating cold water in the middle of the desert so that you can’t take a cold shower. On the other hand, I guess you save on gas consumption by not needed to heat as much (gas comes from delivery trucks, not gas lines, kind of like living in the boonies in the 'States). The cistern is plumed inline with the city water system; any time city water is available the cistern will top off automatically. The house water is drawn from the cistern, and pressure is maintained by a pump and accumulator system, probably the same as people in the 'States with wells (anyone?) or who live on mountains. Of course, if you lose electrical power, then you also lose your water. If your cistern is on the roof, you’re going to have at least a little pressure when there’s now electrical power, but with the water rationing and everyone’s cistern filling at the same time, there’s often not enough city pressure to fill your roof-mounted cistern, meaning you need yet another pump to ensure that it gets up there.
It seems that if the city ran just a couple of big pumps on a water tower, the requirement for everyone to have one or two pumps in every, single house could be eliminated. There’s be potable water when there’s no electricity. Cold water wouldn’t make it to tea-making temperatures. And as it is, I don’t know the point of these rolling water-blackouts. Our little 450 liter cistern is plenty for a whole day’s activities, including washing the patio and driveway (they do that here). There’s no conservation. There’s no net savings, and a whole lot in inconvenience, e.g., I didn’t mention that if your cistern runs dry and your pump doesn’t have a water level interlock, it will run until it burns out. Lake Huron water, how I miss thee.
There’s a wacky little short one I saw once near where I’m buying my house - you climb this hill in a very residential neighborhood, house house house WATER TOWER house house house. It was extremely strange the first time I saw it! Anyway, this one is short - water-tower sized, but only maybe a little taller than the surrounding houses. What’s up with that?
My folks live in a rural neighborhood with a local well and non-elevated storage tank. When they lose electricity they very quickly lose water pressure.
The water tower only needs to be a little higher than than the highest building it serves. And this is total height, not height above the ground. So if it’s already on the top of a hill, you wouldn’t need to get much higher.
Heh, water towers. As a kid, I always wondered why almsot every other town had them except mine. I came to find out it’s because my town already had one, just not in tower form.
My town is on the side of a mountain, and has a very high water table. So they just put a large resovoir on the side of the moutain, and since it was already so high up, it didn’t need to be up on stilts. And, since the water table was so high, even on the moutain, the pump still didn’t have to do much work to keep the thing filled. Very handy. And the view from the top of it? Amazing! 
If you have several wells and several water tanks, you can have them all on the same system if each tank has the same overflow elevation. Meaning that, on the lower elevation side of town the tank may be 200 ft in the air, while on the highest end of town you may be able to situate it on the ground.
Oak Ridge TN has their water treatment plant and storage ‘tanks,’ covered reservoirs, on mountain top.
Plenty of warter on tap at a constant pressure for quite some period of time.