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Every foot of height you put under a column of water gives you 0.433 lb per square inch of free pressure.
Caleb Greer shows how to build a gravity-fed rain barrel system using three 55-gallon drums stacked up a wall, delivering free water pressure with no pump or electricity.
Key Takeaways
- Elevation, not pumps, creates usable water pressure; raise barrels as high as safely possible.
- A properly built rack and food-grade containers are essential for safety and water quality.
- Rainwater capture can supply most outdoor watering needs and substantially reduce municipal water bills.
- A first flush diverter and regular cleaning prevent contamination and sludge buildup.
What the video covers
- Head pressure: every foot of water height produces about 0.433 PSI, the same principle as city water towers.
- Rain captured from a roof lifts thousands of gallons to roof height for free, providing a renewable supply.
- Most rain barrel setups fail because barrels sit too low; raising them creates usable pressure.
- Historical precedent: Roman aqueducts and pre-electrification windmill tanks used gravity to distribute water.
- Rain math: 1 inch of rain on 1,000 sq ft of roof yields about 623 gallons, so a 2,000 sq ft roof can produce tens of thousands of gallons yearly.
- Build details: food-grade HDPE drums, uniseal gaskets for overflow and outlet holes, and a load-bearing rack on posts set in concrete rather than the house wall.
- Plumbing uses a cascade of barrels with overflow pipes, plus a first flush diverter to keep water cleaner.
- Applications include drip irrigation, livestock troughs, an outdoor wash sink, and a downspout turbine charging a battery for lights.
- Limitations: roof water is not drinking water, pressure is modest, and structural safety of the rack is critical.
- Promotional segment: the creator mentions a paid book of 126 methods and his website, then returns to the build content.
Chapters
- 00:00Introduction and the physics of water pressure
- 00:55Rain capture potential and channel intro
- 02:09Why most rain barrels fail and historical examples
- 03:14Rain math and sizing your roof capture
- 05:16Building the barrels and fittings
- 06:17Rack construction and structural safety
- 07:24Plumbing cascade and first flush diverter
- 08:37Applications, limitations, and closing
Full Transcript — Download SRT & Markdown
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That is the same physics that keeps the water running in your kitchen when the city pumps are off because every municipal water tower in America is nothing more than a giant barrel held up in the air. I built my own version on
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the side of my house with three blue 55-gallon barrels, a pile of black PVC, and the rain that falls on my roof. The top barrel sits 11 ft off the ground.
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That gives me close to 5 PSI at the bottom spigot with no pump, no electricity, no float switch, and no bill. It runs a 40-ft drip line to my garden, it fills a livestock trough across the yard, it feeds an outdoor
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wash sink, and every time a storm rolls through, a little turbine in the downspout dumps power into a 12-V battery that runs my path lights all night.
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1 in of rain on my roof puts 1,200 gallons of water up on that wall. Last year that roof caught over 50,000 gallons. I did not pay for a single one of them. Before we get into it, everything I cover on this channel,
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every system, every build, I put in one book. 126 methods, sourced and tested. Caleb Greer offgrid.com.
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That is all I will say about it for now. Here is why this works and why almost nobody sets their rain barrels up this way. Water is heavy. 1 gallon weighs 8.34 lb. A full 55-gallon barrel weighs about 460 lb. When you lift that weight
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off the ground, you are storing energy in it, the same way a hydroelectric dam stores energy behind the wall. The higher the water sits, the harder it pushes on everything below it. Engineers call that head pressure, and the math is
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dead simple. Every foot of vertical height equals 0.433 PSI. 10 ft, 4.3 PSI. 23 feet, 10 PSI. A city water tower standing 120 feet above town delivers about 52 PSI to every faucet in the system, and it does that
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with zero pumps running at the moment you turn the tap. The pumps only work at night refilling the tower when power is cheap. The tower does the rest with gravity. Now, look at your house. You have a roof that is anywhere from 10 to
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25 feet in the air. Every time it rains, nature lifts thousands of gallons of water up to that height for free. Then your gutters and downspouts throw all of that stored energy straight onto the ground. Most people who own rain barrels make it
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worse. They set one barrel on a couple of cinder blocks, maybe 16 inches off the dirt. That gives them about 2/3 of a sigh. You open the spigot and the water dribbles out like a leaking garden hose.
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They try to run a soaker hose off it and nothing happens. Then they decide rain barrels are useless. The barrels were never the problem. The height was.
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People figured this out thousands of years before electric pumps existed. The Romans moved water into their cities on aqueducts that dropped only a few inches per 100 feet of run. Fed fountains, public baths, and private houses, and never used a pump. Farms across America
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ran on the same idea for a century. Before rural electrification reached most of the country in the 1930s and 40s, a windmill pumped water up into a wooden tank on a tower next to the house and gravity sent it to the kitchen. The
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barn and the stock tanks for days after the wind died. A lot of those tanks are still standing. That tank was a battery.
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It stored the windmill's work as water up in the air, and it paid that work back out every time somebody opened a valve. My barrels do exactly the same job. The only difference is that I let the clouds do the pumping instead of a
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windmill. Here is the rain math so you can size this for your own roof. 1 in of rain falling on 1,000 sq ft of roof is 623 gallons. Not a drizzle, a real measured gallon number. My roof footprint is about 2,000 sq ft and I am
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in a spot that gets around 50 in a year. That is over 62,000 gallons a year landing on my house. Even if you capture only the downspout on one side, you are looking at tens of thousands of gallons
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and every one of them arrives already lifted to roof height. Rain does not stop. Every storm refills the system.
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That is your unlimited supply. You will never run out of sky. The EPA estimates outdoor watering makes up about 30% of household water use across the country and in dry western states, it can climb to 60% in summer. That is the water you
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are paying the city for, treating to drinking standards and then spraying on tomatoes. This system takes that bill to zero. Here is exactly how I built it.
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Start with the barrels. I used three food-grade 55-gallon HDPE drums, the blue ones you see at every farm supply and on every classified site. They came out of a bottling plant and cost me $10 a piece. Car washes and food plants give
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them away for free half the time just to get rid of them. Only buy food-grade drums and ask what they held. Juice concentrate, syrup, olive oil, all fine.
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If the seller does not know or it held anything chemical, walk away. Wash them out with hot water and dish soap, then a rinse of 1 cup of bleach and 5 gallons of water and let them air dry with the
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lids off for a day. Each barrel gets three holes. A 2-in hole near the top for the inlet, a 2-in hole about 4 in below the rim on the opposite side for the overflow, and a 3/4-in hole 2 in up
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from the bottom for the outlet. Every hole gets a bulkhead fitting or a rubber uniseal. A uniseal is a rubber gasket that pushes into the hole and grips the PVC pipe so tight you can stand on the joint and it will not leak. They run
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about $4 each and they are the single best upgrade you can make to a rain barrel build. No glue, no silicone, no thread stripping out of thin plastic.
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Now the most important part of this whole project, the rack. Three full barrels weigh close to 1400 lb. You cannot hang that off siding. You cannot hang it off a few lag bolts into studs.
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If it lets go, it rips the wall open and 1400 lb of water and plastic coming off the side of a house will kill whoever is standing under it. Everything you see on that wall is carried by the ground, not
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the wall. I set four pressure treated 4x4 posts in concrete, 2 ft deep, tight to the house. Then I built three platforms on those posts out of doubled 2x6 lumber. Each one stepped up about 32 in higher than the one below, so the
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barrels climb the wall in a staircase. Each platform carries its full barrel on its own posts. The house only gets a few galvanized straps at the top to keep the rack from leaning. That is the trick to making it look like the barrels are
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hanging on the wall. The wall is only steadying them. The posts are holding them up. The bottom of my top barrel sits at 8 ft and the water surface inside it sits at about 11. Now the plumbing. This is where it becomes a
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cascade. I cut the downspout at about 9 ft and installed a rain diverter, a fitting that sends water out a side port into a 2-in pipe running to the inlet of the top barrel. Before it gets there, it
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passes through a first flush diverter. That is a vertical length of 3-in PVC capped at the bottom with a small floating ball at the top. The first few gallons off a roof carry all the dust, pollen, bird droppings, and shingle grit
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that collected since the last rain. That dirty water fills the vertical pipe first. When the pipe is full, the ball floats up and seals it off, and everything after that is clean water going straight into your barrel. A slow
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drip hole in the cap empties it between storms, so it resets on its own. Total cost, about $15 in PVC. Build one. Your barrels will stay clean for years instead of filling with sludge in a single season. The top barrel fills
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first. When it is full, water rises to the overflow and spills out through a 2-in pipe that runs down the wall into the inlet of the middle barrel. When the middle barrel fills, its overflow drops into the bottom barrel. And when the
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bottom barrel is full, its overflow runs out along the base of the house and away from your foundation. That is what those black pipes zigzagging down the wall are doing. Every barrel fills automatically, top to bottom, every storm, without you
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touching a valve. Here is the part most people miss. Each barrel holds water at a different height, so each barrel gives you a different pressure. The bottom barrel, sitting about 2 ft up, gives you a gentle 1 to 2 PSI, perfect for filling
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watering cans and buckets. The middle barrel gives you around three. The top barrel is the power source. I ran its outlet through a 3/4-in line straight down the wall to a manifold at ground level. That line carries the full 11 ft
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of head, close to 5 PSI, and that is what drives everything else. Now, what that pressure actually runs, drip irrigation. Standard drip emitters are built for 15 to 30 PSI city pressure, but gravity drip kits with low pressure
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emitters are made to work on 1 to 5 PSI from a tank. I run 40 ft of 1/2-in drip line with emitters every 12 in along three raised beds. I open one ball valve in the morning, and the whole garden
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waters itself. No timer, no pump, no extension cord across the yard. Livestock water. A 100-ft run of 3/4-in poly pipe crosses the yard to a stock tank with a float valve. Gravity keeps the trough full. When the goats drink it
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down, the float drops, the valve opens, and the barrel tops it back up. The outdoor wash sink. A plain utility sink on a post next to the garden, fed straight from the top barrel. You can wash vegetables, rinse muddy boots,
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clean tools. 5 psi feels like a weak faucet indoors, but for a garden sink, it is plenty, and it never shuts off when the power goes out. Toilet flushing. If you run a line inside, a gravity-fed toilet tank refills fine on
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low pressure. It just fills slower. During an outage, when the well pump is dead, that is a working toilet. And now, the electricity. During a storm, the downspout is the most violent water on your property. A heavy rain of 1 in an
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hour on one side of my roof sends roughly 10 gal a minute down that pipe, falling 9 ft before it ever reaches the diverter. Instead of letting that energy hit the ground, I put a small inline micro hydro turbine in the downspout.
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You can buy these as 12-V water turbine generators online for about $25. It is a little impeller and a permanent magnet generator in a plastic housing.
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Water spins it, it puts out 12-V DC. That runs through a cheap solar charge controller into a 12-V battery. Every good storm pushes a charge into that battery, and that battery runs a string of LED path lights all night, charges
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phones through a USB socket, and keeps a small radio alive when the grid is down.
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It is not running your fridge, and it is not running your house, but it is power from your roof that you got for nothing every single time it rains. Total cost breakdown. Three food-grade barrels, $30, or free if you ask around. The rack
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I built from leftover 4x4s and 2x6 from an old deck tear out, plus a bag of concrete and a few straps, about $20.
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Uniseals, $12. PVC pipe and elbows, $25. First flush diverter, $8 in scrap PVC. Downspout diverter, $12. Ball valve and two spigots, $15. Total for the full cascade, about $120.
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Want the extras? The gravity drip kit is about $30, and the downspout turbine with a charge controller and a small battery is around 60. A typical electric booster pump for rain barrels runs $150 to $400 for the pump alone. Before you
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buy a single barrel, it needs a power outlet outside, and it quits in an outage. This system costs less than that pump and has nothing to plug in. A few build details that matter more than they look. Screen every opening. Mosquitoes
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can breed in standing water in about a week. Fine stainless mesh over the inlets and overflow vents, and tight lids on every barrel. A teaspoon of food-grade oil on the water surface also stops larvae if you ever see them. Block
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the light. Blue barrels already block most sunlight, which is why they are blue. If you use white or translucent barrels, paint them dark or wrap them, or you will grow algae in a month. Lock the lids. A full barrel is a drowning
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hazard for small kids and pets. Screw-down lids, no open tops. Let it breathe. Every barrel needs a small vent at the top, or air locks will stop your cascade from filling and draining properly. And watch your foundation. The
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final overflow has to carry water at least 6 ft from the house. You built this to stop wasting rain, not to flood your basement. Now, the honest limitations. First, this is not drinking water. Roof water picks up everything on
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your shingles. For the garden, livestock, washing, and flushing, it is perfect. If you want to drink it, that is a separate filtration and sterilization system, and I cover that in the manual. Second, freezing.
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If you live anywhere with a hard winter, drain the system before the first freeze. A barrel that freezes solid can split, and frozen PVC cracks. Leave the bottom spigots open and disconnect the downspout diverter for the winter.
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Third, check your state rules. Rainwater harvesting is legal in every state, but a few put limits on it. Colorado, for example, caps residential collection at two barrels with a combined 110 gallons.
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Most states have no limit at all, and some actually give you a rebate for installing barrels. Fourth, pressure is limited by height. 5 psi is enough for gravity drip, troughs, and a wash sink.
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It will not run a pressure washer or a standard impact sprinkler. If you want more pressure, go higher. Every extra foot is another 0.43 psi. Mount a fourth barrel at roof height, and you are pushing seven or eight. Fifth, the
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turbine only works when it rains. It is a storm charger. If you get long dry stretches, your battery will drain. Pair it with a small solar panel on the same charge controller, and the battery stays topped off rain or shine. If you want to
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scale it up, the principle does not change. Swap the 55-gallon drums for a 275-gallon IBC tote on a heavy timber platform, and you have five barrels in one container.
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Put two totes up on a 6-ft stand at the top of a slope, and you can gravity feed an entire market garden. Some homesteaders run a 1,500-gallon tank on a hillside 30 ft above the house, and get 13 psi to every outdoor faucet on
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the property with no pump at all. Same physics as the city water tower. You are just building it to your size and this pairs perfectly with everything else on this channel. The solar air heater handles your daytime heat, the pellet
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stove handles your nights, the barrels handle your water. None of them need the grid. Think about what is really happening here. Every time it rains, nature lifts thousands of gallons of water onto your roof and hands you the
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energy for free. Most people send it straight down the drain. You catch it, you hold it up high, and you let gravity do the work a pump would do for the rest of the season. Water at pressure, garden
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on autopilot, animals watered, lights on at night, and the rain fills it all back up again next week. It never runs out.
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If you want every one of these systems in one place, step-by-step, it's at calebgrieroffgrid.com.
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Links below. How many gallons do you think your roof dumps on the ground every year? Grab your square footage and your local rainfall and do the math, then drop the number in the comments. I want to see who has the biggest free water tower on
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the channel. I will see you on the next one.
Topics:rain barrelgravity water systemoff-grid waterrainwater harvestinghead pressureDIY irrigationfirst flush divertergravity drip irrigationhomestead watersustainable living
