Tinaco: Mexican raised water tank
The final architectural
tidbit which caught my fancy during our Mexican
adventure was the raised water tanks (known in Mexico as tinacos.)
We noticed these last year during our drive through the city of Merida,
and were surprised that such an archaic method of producing a
household's water pressure would be found in the heart of the
city. (Not that I have anything against archaic systems --- we
have a gravity feed
water system much
like it on our farm.)
Although the internet is a
bit vague on the purpose of tinacos, my understanding is that
cities in the Yucatan have municipal water systems, but that you can't
count on them to always be operating. Added to that, the Yucatan
has frequent floods due to storms from the ocean, at which point the
city water is muddy and unpotable.
A tinaco equalizes out these problems
by providing a backup supply of water for the household. Every
evening, Mexican families use the pressure of the city water to fill up
their tinaco,
and then water passively falls from the tank to fill their toilets,
washing machines, and sinks throughout the day. Since the most
commonly used tanks hold 290 gallons, a family can easily go a day or
two without hooking into the municipal system if the water is turned
off or is dirty.
One
article also notes
that the city water may not provide enough pressure to fill your tinaco in certain locations,
in which case you'll end up with an elaborate system like the one shown
above. The city water trickles into a buried cistern, then is
pumped up into the tinaco as
needed, a bit like self-sufficient U.S. homes might fill up a bladder
tank with well water to provide pressure without running the pump
continuously. I like the low tech solution, but I wonder what
their water pressure is like?
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You need 30 feet of height to get one bar of water pressure. Looking at the height the tank sits, I'd say the pressure is not much.
Out water mains here are supposed to have two bars of pressure.
But for a tap you don't need much. It is just that with lower pressure you need bigger pipes to get the same volume flow. Just look at a typical old-fashioned toilet with the reservoir close to the ceiling. Those flush really well, using a pipe that is about an inch thick.
Faith --- That's right along the lines I was thinking. I love looking at "less developed" countries for tips on how to survive when the power goes out.
Roland --- I was looking into water pressure a month ago when Mark and I first started thinking about bladder tanks. It seemed like there's a wide range of acceptable flow rates in municipal water systems, maybe because of different pipe sizes? It seemed like our flow rate (1 gallon per minute) was in the realm of ordinary, but at the low end. Can you do a quick conversion for me and tell me what flow rate you'd get at 1 bar of pressure with one inch pipe?
Warning: Maths ahead
Assuming laminar flow for the moment, according to the Hagen-Poiseulle equation (only valid for laminar flow!), volume flow is:
Q = ΔP·π·d⁴/(128·μ·L)
For laminar flow, the Reynolds number should be <2300;
Re = Q·L/(ν·A)
where
For 30 meters (100 feet) of pipe, this gives 0.034 m³/s (9 gallons/second).
Now we need to check our assumptions! With this flow, the Reynolds number is 2·10⁹. So in this situation there will not be a laminar flow, and the above calculation is invalid.
So now you need to use the Darcy-Weisbach equation to determine the volume flow. This is where it gets complicated. For this calculation you will need to know something about the roughness of the inside of the pipe, to get at the Darcy friction factor, which depends on the Reynolds number, which depends on the volume flow.
Calculation now becomes an iterative process.
You can use this online calculator to play with the numbers. For a 30 m long 1 inch pipe, you'd get around 0.0015 m³/s (0.4 gallon/s) for a 1 bar pressure loss (assuming a friction factor of 0.019).
Here in the Netherlands, water pipes in homes are typically 10 mm inner diameter. For the same length of pipe and pressure, that would yield 0.00015 m³/s (0.04 gallons/second).
Keep in mind that bends in the pipes (especially right angles) can have as much resistance as several yards of pipe (depending on flow rate, diameter etc.)
For pumping water from the creek, you might want to look at a hydraulic ram as an alternative to an electric motor driven pump. It can use the kinetic energy of flowing water to pump water up. It's main benefit is it's simplicity; it has only two moving parts, and can be made from very basic materials.