Author Options:

Fluid dynamics: can you connect 55-gal barrels in series to lawn sprinklers to circulate and keep emergency water fresh? Answered

I saw several Instructables about how to use barrels to collect and store rain water.  It doesn't rain enough where I live for this to be practical -- however, I have five blue 55 gal barrels that I use to store water for emergencies. I would like to hook all these together with PVC and run my lawn sprinkler system through them, so that the water stays fresh and drinkable. As it stands, I have to store the water with bleach, and dump it all out every 6 months and start all over again. Big waste, and a bigger hassle. Often as not, I am sitting on 275 gallons of undrinkable swamp water at any one moment in time! -- My question concerns the physics surrounding the fluid dynamics. Is this workable -- running PVC between each barrel in series? -- or does that reduce the pressure to zilch at the end, so pressure wouldn't be high enough to water the lawn and garden? Would you have to put a bleeder valve in the top of each barrel so you could completely evacuate all the air? I really hope someone has actually done this, so I don't waste my time and money making something Mr. Wizard would just laugh at!



7 years ago

Finding this feed was exciting to me.
I have a similar desire to hook up my water storage barrels to my incoming water source to my house. I too want to be able to keep my storage water fresh and drinkable and eliminate the waste and hassle as wobryant stated.
I thought to connect the barrels to my incoming water source to my house before it goes into my water heater and hook up the barrels to each other, then connect it all back up to the system that connects again to the pipe feeding the water heater.
In essence, it's kind of just a diversion from the incoming water thru the barrels and then back to the water heater.
Is this a possibility?

It's been a YEAR since I first posted my question, and I thank Randy in Tucson for sending me a personal inquiry yesterday, asking whether I had any further insights on this project. I think what I have to say will be an answer to DIYer2, and also address some of the misconceptions several had about what I was asking.

I have been cogitating about actually getting this project done recently, especially since Japan's tsunami. I live in Southern California, and the specter of a significant earthquake disaster is always on our minds here.

Randy (in Tucson) was thinking about using a series of several 60 gal hot water tanks to store his emergency water supply (not hooked up to gas), which he thought would be cheaper than buying expensive galvanized pressure tanks. He would have these hot water tanks either in series, or in parallel with individual shutoffs to isolate them. He was also thinking about using a small electric pump to dispense the stored water into his home water system.

Since recent events have jangled my own personal alarm bells -- I thought I'd share some of my answer back to him, and hopefully get someone with expertise to respond if my thinking is faulty.

First -- let me be more explicit about how my existing water system is designed. I have a 1-inch water service line coming from the water meter to the house. My lawn watering irrigation system taps off the riser before the riser enters the house plumbing system. The riser has a gate valve so the house supply can be shut off, but still leave on the water supply to the lawn sprinkler system.

The tap off the riser for the irritation system comes out of the ground to an above-ground (18 inches) pressurized anti-siphon vacuum breaker assembly. There are two gate valves there, one on each side of the breaker. The line then goes back underground and feeds each of the individual electric sprinkler control valves. Immediately after each sprinkler valve there is an atmospheric anti-siphon valve assembly.

MY INITIAL PLAN WAS TO INSTALL A NUMBER OF 55-GALLON WATER BARRELS IN SERIES, as an emergency water storage system, that would be flushed with fresh water, anytime the lawn got watered.

I commented to Randy that his plan to use a small electric pump is a little more ambitious than what I had in mind. First, I have a two-story home, so it would probably require a BIG electric pump. Also, water won't flow out of his extra hot water tanks unless water flows in. You would have to have a way to turn off the water supply to those hot water tanks, and then have a valve to let air bleed in. Otherwise he couldn't pump water to the house supply. Do building codes allow for such a configuration? I don't know.

I hadn't actually thought about integrating water storage tanks within my house system, but that deserves further thought. At first blush, I see some pros and cons doing that, versus having the water barrels (55 gal) I was proposing to integrate in series within my automatic lawn sprinkler system.

The main negative I see with his house-integrated emergency water storage system is that, if there were ever to be a disaster resulting in loss of water delivery, or contamination of the water supply, the unknown ambiguities surrounding the projected time when service might be restored make me think I would want to have "drop-by-drop control" over what would then be a very precious, life-saving commodity. With an electric pump, presuming there was still electrical power, someone could inadvertently flush a toilet and waste gallons of water for nothing.

One of the concerns expressed in these responses here about my lawn sprinkler-integrated system was that the materials I proposed to use might not hold up to the water pressure from the city supply, and if any component failed/ruptured, I would have a high-flow water disaster. Not true. The lawn sprinkler system only connects to the city water supply when the electric valves are turned on by the timer. There's no more risk here than there would be if a sprinkler valve were to become stuck in the "ON" position -- and I'm living with that risk NOW, even without adding in a few water barrels.

Also, under my system, the water barrels would never see the constant, high, static water pressure from the utility's delivery system. The only time water would flow, is when the sprinkler timer turns on the sprinkler control valve. And since the system leads to multiple open lawn sprinkler heads, the system is never pressurized like it would be if there was a faucet to turn off on the efferent end.

That seems to be a "con" using Randy's or DIYer2's house-integrated approach, unless I spend BIG money for an appropriately designed water "tank", designed to handle the pressure. Connected to the house system, you would have to have something that could handle the constant water pressure from the water main. My system is low pressure, and intermittent.

I did like all the discussion about potential water contamination and mention of multiple shut-off / bypass valves, but for different reasons than have been mentioned here. One big concern I have, is that I want to be able to isolate my emergency water supply to protect it from contamination that may potentially come -- NOT FROM ME -- but from the city water system. In the event of a bacteriologic mishap, or an overt act of terrorism, if the utility's water supply becomes contaminated, then an emergency water supply system that is constantly connected to the utility, might become contaminated before you become aware of the problem, or before you can return to your home to take proper action to isolate your emergency water supply.

So... if I designed an outside system integrated into my lawn sprinklers, I could have two separate storage systems (A & B) running in parallel, each with a number of water barrels connected in series. Only A or B would be open to receive flow-through when the sprinkler valves were open. In a perfect storm, where local electrical power was lost, and the utility's water supply became contaminated, but the water delivery system remained intact (i.e., delivering contaminated water), a house-integrated emergency water storage system might potentially become contaminated. In my sprinkler-integrated system, both A and B would be isolated from contamination, because exposure requires electricity to run the timer and to open the sprinkler control valves.

In a worst case scenario for me (i.e., electricity on, water on, but water contaminated) the worst thing I would suffer is contamination of half of my emergency water storage supply. (Am I sounding a bit too paranoid here?)

So, unless I'm still missing something about why my system might compromise the purity of the city water supply, I don't think it would. However, I appreciated the warnings made about potential code violations and back-flow contamination of the city water supply, because they caused me to think of an element I hadn't considered.

The stagnant water sitting in the PVC pipes buried in my lawn has the potential for contamination from such elements as run-off from dog feces, etc. via the sprinkler heads in the lawn. But as far as I can see, the pressurized anti-siphon valve in my system will prevent backflow from the irrigation system. I can't see how integrating a series of water barrels into that system would defeat either the function of the combination of atmospheric anti-siphon valve located just downstream from the sprinkler valve, plus the pressurized anti-siphon valve located further upstream between the beginning of the irrigation system, and where it connects to the supply line from the water main that feeds my house supply. Seems like both my house plumbing system and the utilitiy's water main are protected, even in the event of a temporary loss of pressure in the utility supply. Sure, any anti-siphon valve system can fail, but my water barrels pose no increased risk to the community than anybody else's lawn sprinkler system, does it?

SO WHY AM I DREDGING UP THIS OLD DISCUSSION??? ...Because I need more advice.

The point I hadn't considered before, is that backflow from the PVC pipes could potentially contaminate the water I'm storing in my emergency water barrels. I'm thinking that to avoid that possibility, I need something else in my design -- like another anti-siphon valve AFTER my last barrel, to avoid reverse flow from sprinkler heads >> through underground PVC pipes in the sprinkler system >> and into my barrels. If so, at what height would that have to be placed? Higher than the level of water in the barrels? Or just higher than the highest sprinkler head in the lawn?

And another question -- what is to stop the continued gravity-fed flow of all the water in my barrels out through the sprinkler heads once the sprinkler control timer turns the valve off? Will water stay in the barrels, as long as there's no air leak anywhere in the system between the sprinkler valve and the last barrel?

If that's the case -- all the more reason to have a storage system A, and a storage system B, which can each be completely isolated with bypass valves.

Since my expertise is not in mechanical engineering, my ideas might have obvious flaws that won't become apparent to me until I can find some schematics to understand just how an atmospheric anti-siphon back-flow-preventing valve even operates. But I'm sure one of you guys will know the answer off the top of your heads, so I appreciate any help offered. I think there are a lot of people out there who would be very interested in building this system, once all the kinks are worked out.

Bill, in Southern California
(and about 20 miles from the two San Onofre nuclear reactors, as if the risk of earthquake disaster alone weren't bad enough!)


8 years ago

The static water pressure of a gravity-fed system is merely a function of the vertical distance between the opening of the hose and the top of the water level in the tank. The pressure of a column of water is approximately 15 psi for every 32 feet of height. Five barrels connected together as you describe will have essentially no impact on the water pressure because they will be a unitized tank with a surface area five times that of a single barrel but with the height remaining unchanged.
Factors such as pipe size also come into play when you worry about flow rates. Then the cross-sectional area of the pipe, the flow rate and the fluid viscosity (water) will have an effect on the delivered pressure. The drop in pressure is inversely proportional to the cross-sectional area, directly proportional the length of the pipe an directly proportional to the flow rate.
To sum it up, the water pressure you would have is the same as if you were only using one barrel.  Probably not nearly enough to operate even a single lawn sprinkler.

So sorry if I misled you Burf.  Excellent answer for a static gravity-fed system.  What I am proposing is putting the 5 barrels (in series) "in-line" with the utility-supplied water system.  So that is where the water pressure will be coming from -- not gravity, but from the "down-regulated" pressure from the street.  (It's about 110 psi before the pressure regulator, and about 70 psi on the house side - so I don't blow my house pipes.)  So that's what pressure the first barrel will "see".  I'm not educated enough in physics, but it sounds like YOU are -- to know whether, in the process of water going through a narrow PVC pipe, then into a drastically expanded volume of space at each barrel (essentially a 3-1/2 ft diameter pipe), then into another relatively small PCP pipe, then back into the next barrel, etc. -- DOES THAT scenario progressively reduce either pressure, flow, volume, or whatever, by the time the water enters my existing underground automatic lawn sprinkler system?  I'm trying NOT to store stagnant water in a static gravity-fed system.  I'm trying to see if it is plausible to incorporate the five 55-gal barrels into the utility fed water system to flush the barrels with fresh water from the utility every time my sprinklers turn on.  What do you think?  Would it work?

You said:  "The drop in pressure is inversely proportional to the cross-sectional area, directly proportional the length of the pipe an directly proportional to the flow rate..."  So, if my thinking is not flawed, what goes in, must come out, so I presume flow rate would be constant.  The length of the pipe is a constant, since this grouping of barrels would be in-line with existing flow.  So since the cross-sectional area increases each time the flow opens into the next barrel, do I understand correctly that the pressure would drop (to an inversely proportional degree)?  Then does the pressure suddenly recover-- essentially to what it was before it entered the barrel from the pipe on the afferent side (minus a small loss due to the 2 foot length of "pipe" (barrel, actually)? 

(Thanks for your help on this.)

Okay, I think I understand what you are asking now. I attached a drawing to illustrate what I will tell you here.
First, let me specify that hydraulics is not my specialty, but yours is a fairly basic question and the answer is also fairly basic.
Your  proposal is to use 5 barrels as a unitized pressure tank, and your concern is whether the outflow rate will be sufficient to utilize as you would the normal household water system. The answer is a qualified, yes. I say qualified because there are some concerns about the method and materials you intend to use:

1) I question the ability of the barrels integrity and strength to act as a pressurized system for a prolonged period of time. I believe their life span under such conditions would be compromised.
2) You don't discuss in detail the method of connection between the barrels and this will surely be a weak link in the system, if not properly designed and installed.
3) You must incorporate several safety features into your design in order to prevent damage, contamination issues and comply with building code requirements. Among these are incorporating pressure and backflow prevention devices and system isolation.

I know this is a DIY type site but a 275 gallon flood backed by a full flow of water is not a pretty picture. I would strongly suggest you consider buying a manufactured pressure tank and review the overall design with a qualified professional.

Pressure tank.png

It is against plumbing codes to connect a treated water source to any source of untreated water.

In the event of zero water pressure like when there is a break in the pipes, the untreated water will be drawn into the system and pollute it.  It could be dangerous and make a lot of people sick.

It sounds like the water can't flow back to the street main due to the presence of a regulator in the line, but that won't stop the house pipes becoming contaminated.

A regulator won't stop the back flow.  A vacuum breaker would but they don't always work and freeze up.

I guess I don't understand your plumbing. I would think that if the pressure on the street side is higher than the pressure on the house side, the water couldn't flow that way. Unless the street pressure dropped for some reason?
Anyway, I think we 've got the contamination point across.

Pressure drops anytime the line is broken to repair, or add a customer etc.

.  Re-design is talking about the rare, but potentially very dangerous, condition when pressure in the supply lines is lower than at your house. Eg, break in supply piping. You water supply company should have installed an anti-backflow regulator near the meter.
.  Unless you have a high flow rate, varying pipe sizes will not make much difference in pressure. The smaller PVC piping will introduce some resistance to flow, but if you keep the diameter close to your other piping (or larger), you should be OK. For all intents and purposes, the barrels aren't even there.
.  I'd suggest alternating inlet/outlet piping on the barrels. Eg, supply into top of first bbl, outlet of first bbl exits at bottom and feeds bottom of 2nd bbl, exit of 2nd bbl at top and feed top of 3rd bbl, ...

Between what Burf has written and your reply, it seems that your question is answered. I'm wondering how you plan to control the flow into the barrels? Obviously there will be a manually operated tap or valve of some kind to allow the water to be shut off while working on the installation, and the flow will be automatic as the sprinklers switch on and off. Have you thought about a one way valve between the manual shut off and the istallation to prevent backflow from contaminating your house water?