How to Build a 6000 Gallon Water Tank




Introduction: How to Build a 6000 Gallon Water Tank

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The idea of "being prepared" can involve so many things in so many different situations. The key is to ask yourself what you cannot, or do not want to, live without. For us, the answer is water.

Whether you live off-grid or in the city, having rain water catchment and a tank is not a bad idea, if only as a backup. Most urban water reaches the home using electricity, so if the power fails, so does your source of water. Furthermore, there are times when your pipes can freeze, again cutting off your water. If you have a tank on your property, you can, at the very least, go and manually get a bucket of water for general sanitation.

When providing your own water system - whether as your main supply, a backup or for fish or irrigation - the bulk of your efforts should go towards storage, or a tank, as that is the most costly part.

Plastic tanks are easy to set up, but they are very expensive in larger sizes. Concrete ones are durable, but ill advised for any beginner, as they are prone to leaks if not done correctly, especially where the walls and floor meet. We have found that the shell and liner system described in this article is by far the best option for us. It's cheap, easy (even for just two people), and quick.

For information about how to harvest the rain from your roof to fill your tank, see here. For further information on cisterns, click here. For the full article, click here.

Step 1: Dimensions

This article is based on a 16ft diameter, 4 ft tall tank, holding 6,000 gallons. However, you can alter the dimensions to fit your needs.

Round tank:

π (3.14) x radius x radius x height x 7.5 = gallons

(e.g. 3.14 x 8ft x 8ft x 4ft x 7.5 = 6028.8 gallons)

Square tank:

length x width x height x 7.5 = gallons

(e.g. a 18ft square that is 4ft tall will hold 9,720 gallons)

Liner Dimensions:

You want to make your liner a little larger than the tank's dimensions, so that it has some slack. Also make it 1ft taller than your tank's walls.

Even though a square tank is more efficient with space and thus your liner, we would unequivocally recommend going with a circular design. We have done both and the round one is far stronger and requires less work. Any money you might save on the liner for a square tank is negated by the extra strength you will have to add to the frame. If you decide to go square, bury the bottom 1/3 of the tank.

Step 2: Foundation

  1. Mark out the area where you wish to build your tank, and level it. You can dig down or fill in, though a combination of the two is often the least labor intensive.
  2. Put a layer of sand, about 6" deep over the whole area and compact it well.
  3. Place a rebar or post in the center of the area and attach a string to it.
  4. Tie the other end of the string to a stick or piece of metal, so that the distance between the stick and the center post equals the radius of your tank, in this case 8 ft.
  5. Keeping the string taut and the stick upright, mark the sand in a circle around the central post.
  6. Center bricks over this line all the way around the circumference, leveling them with each other.
  7. Fill your circle with sand, then compact it well, so that the sand is an inch or two below the top of the bricks.
  8. Fill that inch or so with finely screened sand and compact again.

Step 3: Walls

  1. Drill 1/8" holes every 6" on a 4ft long strip of metal (there will be 7 holes in total). This will be the jig that you use to drill the sheet metal, so that all your holes line up exactly.
  2. Clamp the jig onto one 4ft side of sheet metal and then drill through the jig's holes into the metal. Make sure that the edges of the metal jig line up well, so that you will get a precise position on each sheet of metal. Repeat this process until all five pieces of sheet metal have holes on both 4ft sides.
  3. Using a 3/8" drill bit, drill out all these holes so that your 3/8" bolts pass through easily.
  4. Stand up two pieces of sheet metal, so that their bottom edge is centered on the ring of bricks, and the holes on the sides line up with each other.
  5. Bolt them together, making sure the bolt heads are on the inside of the circle and the threads on the outside. Start from the bottom bolt to the top.
  6. Continue bolting together the sheet metal until you have completed the circle.
  7. Drive in small pieces of rebar at the base of the walls periodically. These rebar should go in the cracks between the bricks. This will make sure the structure doesn't shift and fall off the bricks.
  8. Paint the metal walls, inside and out, with a quality metal primer and finish paint.

Step 4: Plumbing Part 1

There are three sets of plumbing to consider: the intake (which can go into the tank roof and will be addressed in the roof section of these instructions), the outlet and the overflow.

Outlet: You can make this any size you wish. The larger it is, the faster water will come out, but the more expensive your pipes will be. Generally, pipes to a house are either 1/2" or 3/4". You want the outlet to be as low to the floor as you can get, and in a location that is convenient to wherever you want to use the water. On our tanks, we use 1 1/2" outlet sizes, to be able to hook multiple tanks together.

Overflow: The size of the overflow depends on the source of water that will be filling the cistern. For a rain catchment system, your overflow wants to be able to match or exceed the size of pipes going from your gutters to the tank. At least 3" is recommended, although more if the catchment area is very large and you experience heavy, fast rains. The overflow point will want to go as close to the top of the walls as you can make it. Think about where you want the overflow to go - whether to another cistern, an orchard, or somewhere else that can safely handle the excess water - and place it accordingly.

Please note, that in this system the overflow point and the overflow pipe are 2 different things. Because we have a self cleaning overflow design, the overflow point is actually higher than the pipe hole in the metal wall.
  1. To position the overflow hole (where the overflow pipe goes through the wall), hold a 3" T against the side of the wall. The T should be on it's side, so that the long part is vertical. The bottom of the small side part is the overflow level. Make this about 4 inches below the top of the tank. This is the overflow point. Mark this spot with a marker.
  2. Cut a 4" piece of 3" PVC. On one end of this piece, put a 3" elbow. On the other end, place another elbow, but turn it 90 degrees compared to the first elbow.
  3. Line the top elbow up so the bottom of its side hole is lined up with your overflow point. The bottom elbow should be facing the wall. Draw a circle around the elbow. This marks your overflow hole.
  4. Now, position the bulkhead fitting over this hole, and draw a line around it so that the line is slightly bigger than the threads on the fitting. Cut out this hole.
  5. For the outlet hole, hold the 1 1/2" bulkhead in place, about 1" from the bottom of the tank. Draw a line around the threads of the bulkhead. This is the outlet hole.
  6. Drill out each hole with a metal hole saw. If you don't have a hole saw that fits the size perfectly, use a jigsaw with a metal blade. Drill a 3/8" hole on the inside edge of your line, and then use this hole to start cutting along the line.

Step 5: Liner

  1. Fold five strips of vinyl tarp, 4.5ft long and a couple of inches wide.
  2. Line these strips over each set of bolts, to protect the liner from any rough edges of the bolts. Tuck the bottom of each strip under the sheet metal walls and fold the top over the top of the sheet metal and attach it temporarily to the highest bolt.
  3. Also put a strip of tarp on the top edge of the walls.
  4. Place another piece of vinyl tarp on the floor of your circle, so that your liner will be protected from any little rocks in the sand.
  5. Get out your liner somewhere outside of the tank and fold it in a way that will be easy to unfold in place. This is best done by unfolding completely, then folding the sides towards the center, then rolling the whole thing up from one side to the next. Lift the liner inside the cistern walls.
  6. Position the liner on one side of the tank, then unroll it. Position the bottom of the liner on the floor, so that it meets the walls evenly, then lift the sides of the liner up against and over the metal walls. There should be about a foot of extra liner on the outside of the walls, and once it is all in place, it will hold itself. Make sure to leave a bit of slack on the sides.

Step 6: Plumbing Part 2

  1. From the outside, draw a circle through the outlet and overflow holes in the metal onto the liner.
  2. Cut out each circle, but not all the way to what you marked. Make the liner hole about 1/8" smaller on all sides.
  3. You want the flat part of the bulkhead on the inside of the tank. Unscrew a bulkhead, but leave the grommet in place. From the inside of the tank, push the bulkhead through the liner hole, and then through the hole in the metal. Screw the bulkhead nut in place. Tighten it well and put a bead of silicon around it where it meets the liner.
  4. For the overflow fittings, you don't need PVC glue, especially for the fittings on the inside of the tank. Just push them together.
  5. On the inside of the overflow bulkhead, screw a male thread to PVC adaptor. Cut a 4" piece of 3" pipe, and insert it into the adaptor. Now, take your elbow assembly from step 4, and push the bottom elbow on the pipe.
  6. Cut a 4" piece of 3" PVC and insert it into the top elbow. On the other end of this pipe, push on the T, with the long part vertical.
  7. Measure from the bottom of the T to the bottom of the tank. Subtract the height of an elbow from this measurement. Now, cut a piece of 3" PVC to fit this measurement.
  8. Put an elbow on one side of this pipe, and the other end should go up into the bottom of the T.
  9. With the remaining 3" PVC, lay it on the ground and make a line of 3/8" holes for the entire length of PVC. These hole should be about 4" apart. On the other side of the pipe from this line make a few 1/8" holes, maybe 6 holes for the entire length of the pipe.
  10. Place the 3" cap on one end of this pipe, and the other end can insert into the elbow on the overflow assembly. Make the 3/8" line of hole face the tank bottom. The pipe should lay on the ground, and try and make it go towards the outlet bulkhead as much as possible.
  11. On the outside of the overflow's bulkhead, screw a male thread to PVC adapter. You can then attach PVC pipe to this to take the overflow's water to where you want it to go.
  12. On the outside of the outlet's bulkhead, screw in a threaded nipple and then a valve. From the valve, you can attach pipes to take the water to wherever you want to use it.

Step 7: Roof Support

  1. Lay out two 20 ft and one 10 ft pieces of 2"angle iron. On one side of the angle iron, drill 3/8" holes, one foot apart, about 3/8" from the edge.
  2. On the other side of the angle iron, cut the metal every 6 inches with a chop saw. This will allow the angle iron to bend easier.
  3. Using a small strip of metal as a bridge, weld the five piece of angle iron together.
  4. Paint the angle iron and metal strips with a high quality metal primer and finish paint.
  5. Bend the continuous piece of angle iron to snugly fit the inside of the tank, so that the horizontal part is about an inch below the top of the walls. Mark where it joins itself, remove it and weld it together so that it is a circle.
  6. Put the circle back inside the tank, so that the horizontal part is about an inch below the top of the walls, and clamp it in place.
  7. Hold the 10ft x 2" strips of metal on the outside of the tank walls, level with the angle iron. Through the holes of the angle iron, mark the strips of metal. Remove the strips and drill out the holes using a 3/8" drill bit.
  8. Bolt the strips to the angle iron, removing the clamps as you go. These two pieces of metal not only clamp the liner in place, but the angle iron also serves as a support for the roof.

This roof is designed to allow any rain that falls on it to enter the tank.

Step 8: Roof Frame

  1. You need to make a ring of 3/4" PVC that sits on the angle iron support. Within this ring, place twelve 3/4" Ts alternatively at 37" then at 63". The Ts want to be angled up at about a 30 degree angle. None of this PVC needs to be glued together, which helps to make minor adjustments as you go along.
  2. Cut 6 pieces of 17ft long 3/4" PVC.
  3. Cut 6 pieces of 17ft long 1/2" rebar.
  4. Feed the rebar into each piece of PVC and then place each piece of reinforced PVC into the Ts on the outer circle according to the diagram. As each piece goes into place, the structure will get increasingly strong.
  5. Put a piece of vinyl tarp over your frame and tuck it under the PVC circle. Cut off any excess from the inside.
  6. Do the same with a mesh like hail screen.
  7. From the inside of the tank, screw the tarp and screen to the PVC circle, every 6". Now you can screw the PVC circle into the angle iron.
  8. Cut out a hole for your access door. It wants to be big enough for you to comfortably fit through. Add some extra PVC around the door opening for added support. You can make the door out of any material later, so long as it fits over the opening and is either removable or hinged.
  9. Cut a hole out of the tarp and mesh where you want your inlet pipe to go. Place a PVC elbow (already attached to your inlet pipe if you wish) into the hole.

(NOTE: If you are using the tank for fish, use greenhouse plastic instead of the tarp and mesh, and you are done).

Step 9: Acrylic Concrete

  1. With large brushes on long handles, paint the whole roof with a layer of acrylic, cement and water. You want the consistency to be like sour cream. It will not completely cover all parts of the mesh.
  2. Once the first coat is dry, you can apply the second coat. The second coat wants to be a mix of acrylic, cement and water with sifted sand added. Try and cover the mesh completely with this coat.
  3. For the third and final coat, do not put sand in, just cement, acrylic and water.
  4. Each coat dries fairly quickly. You can add more coats if you wish, but three are sufficient for this purpose. As it cures properly (over a week or two), it will get increasingly hard.
  5. Paint the roof with a white, waterproof paint.
  6. Sweep out the interior of the tank, and clean up any acrylic concrete that may have spilled inside. The tank can now be filled with water and used.

Step 10: Materials

    50 bricks (Compressed Earth or similar)

    5 pieces 10ft x 4ft pieces of 18 gauge sheet metal

    60 x 3/8" X 2" bolts, nuts and washers

    50 ft of 2" angle iron

    50 ft of 2" metal strip

    12 x 3/4" PVC Ts

    9 pieces of 20 ft 3/4" PVC

    6 pieces of 20 ft 1/2" rebar

    18 ft x 18 ft vinyl tarp

    18 ft x 18 ft mesh (hail screen)

    2x 5 gallon buckets of acrylic

    3 bags cement

    1x 1 ½" bulkhead

    1x 1 ½" nipple, 3" long

    1x 1 ½" valve


    Pond liner – potable if needed – 16 ft diameter, 5 ft tall

    Overflow Parts (for this tank, we used 3" overflow)

    1x 3" bulkhead

    2x 3" male thread to PVC adaptors

    3x 3" Elbows

    1x 3" T

    1x 3" cap

    20ft X 3" pipe

Step 11: Tools

    Dirt-working tools (shovel, pic, etc.)


    Tamper or Compactor



    Measuring Tape


    Circular Saw


    1/8" drill bit

    3/8" drill bit

    Crescent wrenches

    Hole saws

    Saw (for PVC)

    Concrete mixing tools

    Large brushes with long handles

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    7 years ago on Step 7

    You can often find an above ground pool for pretty cheap at the end of the season around where I live... might not be good for potable water (might be ok, not sure), but for "work" water, might be something to consider. Get a good deal and it would probably be cheaper than the materials for this. Not as long term tough, but a starting point. The liner could be worth it by itself.

    Just a thought.


    Reply 7 years ago on Step 7

    these would be great liners for irrigating or animals, but it is not rated for potable. Still, it is a great start, and those liners should last a long time out of the sun. Even new, they are considerably cheaper than a potable liner and should be considered as a viable option.



    8 years ago on Introduction

    Nice Instructable. I am planning an off-grid installment. (buying land, building an efficient house, and getting away from everything.) With this, i know you want to keep sunlight out, but how about artificial lighting (ex. sunlight threw a bleach bottle, or candles)?
    my idea is have a pool, aswell.


    Reply 8 years ago on Introduction

    It depends on what you want the water for, but it is generally not a good idea to swim in water that you will drink. If it is for irrigation, then that's fine. The algae will eventually balance itself out, so a bit of light is not the end of the world. If I were to make a pool with this, I'd put a greenhouse covering, instead of concrete.


    Question 1 year ago

    I really love the work you did to create this. I'm curious, do you still use these tanks in 2019 that you build years ago? If so, how's the durability? Have you had needed to rebuild, replace any rusted steel, replace liners?

    Interested in AZ, Sean


    Question 2 years ago on Step 10

    Hey, great Instructable there. I am thoroughly impressed.

    I wanted to inquire, if I needed a 40ft diameter 5 ft high pond liner, any advice on where I can get such? I will appreciate any help towards that. Can't seem to be able to trace a seller.




    Question 3 years ago

    Great project and instuctable,

    What acrylic are you using for your acrylic concrete? Have you experimented with different acrylics?


    7 years ago

    How much did this cost total?


    Reply 7 years ago on Introduction

    At least $582.00 dollars for the 5 sheets of galvanized panels alone. Shipping not included in that--and it will be a bunch, at least 50 dollars. You can't get these sheets at homederpo or lowes or tractorsupply. You may find it at a local contractor-hardware store for building real things vs inside house projects.

    Metalsdepo has them for 120 each, and stainless is more expensive ( Since this instructable has you coat with primer and some rustoleum type paint, one might consider going with the regular steel sheets and save 115 dollars.

    Rustoleum to cover that amount will be another 30-80 in paint depending on the options.

    Tamper is best bought at a harborfrieght for 20 dollars because it's a flat dumb piece of steel on a stick. Same with all the other tools except for the drill bits. Assuming you are tackling this project, it may be best to invest in good solid (diablo, bosch, etc) drill bits, but every other tool in this instructable like brushes, one should try to acquire them as cheaply as one can and toss them if they can't be cleaned.

    For the shovel and pick, again harborfreight. For the pick, dont' get a pickaxe, get a mattock pick with fiberglass handle $22. This is a great piece of tool for cutting roots and absolutely destroying rocks or prying them out. Mattock end is much more useful than shovel for clearing the tank foundation.


    Reply 3 years ago

    For the sheet metal, you could try a commercial air condition installers. They use galvanized sheet metal to make duck work to send air through to everywhere in the building. Just a though..


    Reply 7 years ago on Introduction

    these metal panels cost about $50 each, and I bought them locally at a metal shop.


    Reply 7 years ago on Introduction

    Hmm, the 3 online place I looked had them for over 120 dollars. I wonder what this is all about? I have never heard of online people ripping others off.


    Reply 7 years ago on Introduction

    well, I don't know. They are simple sheets of metal, should not cost $120 a piece. It's just sheet metal, nothing special.


    Reply 7 years ago on Introduction

    Just another thought to expand my last thoughts (sorry this is a long post)... but PVC is awful toxic. I would not line my tank with a pool toy. Rather, it would make sense if you're already investing in a DIY 6k gallon tank to use a better material such as polyethylene. The best material is actually a platinum-cured silicone, which is cost-prohibitive and also not available for this application, except as a spray-on or paint-on (in layers) application. For this I would recommend contacting smooth-on. They have food grade materials. Keep in mind, if you can find a material to act as the 'bladder' or 'lining', you may be able to find something that a food-grade silicone would adhere to, and you wouldn't have to coat more than 1-2mil I wouldn't imagine, to have really 'perfect' zero toxic, zero off-gas water.

    Personally I cannot tolerate any kind of plastic smell in my water, so the choice is to spend money storing filtered water perfectly or perfectly filtering PVC tainted taint-water.

    Here's more info on PSI for choosing materials to use as alternative bladders.

    6000 gallons * 8.34 lbs/gallon = 50040 lbs

    Inner surface of the tank 3.14159 * 96" * 48" = 14476.44672 sq inches

    Base surface of tank = 3.14159 * 96" ^ 2 = 28952.89344 sq. inches (base)

    Total: 43429.34016 sq inches

    50040 lbs / 43429.34 sq inches = 1.15221645 lbs/ sq inch


    I think I did this correctly. You need a liner material that can handle this PSI x 2. (>2.5 - 3 psi)


    Reply 7 years ago on Introduction

    psi is water height (in feet) times .45. In this case, 4 ft x .45 = 1.8 psi.

    liner was engineered for higher
    pressure. I've used these liners to over 10 ft deep, and they can do
    even deeper.

    PVC toxicity is related to UV exposure. The parts
    in contact with water are in darkness. The liner in this instructable is
    rated for potable water.


    Reply 7 years ago on Introduction

    Very useful info, thank you!


    Reply 7 years ago on Introduction

    Total cost is about $1,600

    The liner was $750 (including shipping)
    The metal cost was $300
    The roof was $250
    Plumbing was $200 (including all pipe, fittings, etc)
    Paint and general hardware - $100


    Reply 7 years ago on Introduction

    If you are going to use for just irrigation and not for drinking water, you can save at least $500 and go with a pool liner.


    5 years ago

    π (3.14) x radius x radius x height x 7.5 = gallons

    Hi. I wanna ask. why is it u times with 7.5?


    Reply 5 years ago

    Got it. Its just a conversion unit ?