My rainwater tank array made from recycled plastic drums, 1300 litres capacity
Why Small Size Water Tanks?
Rainwater is a valuable resource that is largely under-utilised in urban environments. It’s one of nature’s free resources that we can use to grow food, and considering that Australia is the world’s driest continent, rainwater is a very valuable resource, far to valuable to let it run down the drain!
You’ll hear many opinions about what size rainwater tanks are “worthwhile” and you’ll hear mention that “anything under whatever size is not worth the effort”, and so on.
Most of this rhetoric is based on the assumption that people have a nice big house (which they own!), with a perfect roof, plenty of free space in the back yard to put in some really big tanks and finally, money to pay for it all.
Let me say, if you’re growing a garden, you’ll need all the water you can get, and every little bit makes a difference. If you can get it for free, it beats paying for it. With water restrictions in Australia, rainwater collection can really make the difference for a garden surviving through a hot summer.
Ultimately, we can choose to utilise the resources that nature provides us for free, as limited as they may be, or we can simply let perfectly good pure rainwater run off into the storm water drain… The choice is ours.
From experience, there is a place for small capacity water tanks in urban environments. Small capacity water tanks work in places such as rental properties, small courtyard gardens, and even big back yards on a budget.
In these situations, the considerations for choosing a water tank are completely different to the big house/big budget scenario.
In a rental property, you may want water tanks that are small enough to transport from place to place, can be dismantled, and can even possibly fit in a regular car for transportation (or a bike trailer for that matter!).
In a small house or unit, the water tanks must be able to fit through any doorways, gates and access paths to reach their final destination in the backyard. Additionally there is only limited space in most small backyards or courtyards anyway.
If you’re on a budget, the main criterion is cost. Just because a person doesn’t have loads of money doesn’t mean they can’t do their part in living sustainably!
You can purchase small tanks and install them yourself, or you can make them yourself out of recycled materials. Cost is the deciding factor here. Even when using recycled materials, the tank fittings usually must brought new, and they can quickly add up cost-wise.
A good friend of mine, David, he’s the water-expert, and he has done extensive research and costing on setting up small tanks to harvest rainwater, and he has come up with some significant findings. In his own words:
“After working on the possibilities I came to the conclusion that going beyond 3 barrels was not really economical. I feel there are better commercial options – or look into buying something second-hand. Five barrels interlocked with stands, overflow and a tap is going to cost approx. $300 in materials. You can buy 1 kilolitre tanks for $200 or less.”
He is suggesting that a setup utilising three barrels is the biggest you would go in terms of cost effectiveness.
David has come up with some great designs for constructing rainwater tanks from interconnected plastic barrels, and with his permission, I’ll present some of the designs in the future.
For now, I’ll share my own designs of the setup with the blue drums pictured in this article.
Modular Water Tank System Construction
Here are the step-by-step instructions for building a modular water tank system which works either as a single tank or as multiple tanks connected together for greater water storage capacity.
It’s all constructed out of a recycled plastic drum and a handful of common irrigation fittings that you can get from most hardware of garden outlets.
First, here’s the basic design:
The following instructions are comprised of three parts:
- The construction of a single tank setup
- Additional steps required for the construction of a multiple tank setup
- Connecting to a pump and further enhancements
Step 1 – Prepare Plastic Drum
Obtain a plastic drum with a lid, to use as your water tank. Clean and rinse out if necessary.
The plastic drum used in these instructions has a capacity of 220 litres (lid not shown in picture below, as it was left off to air-dry after washing it out).
Recycled plastic drum (220 litre capacity)
Step 2 – Gather Tank Fittings
You will also need some tank fittings to construct your water tank.
For the basic single tanks design, you will need:
1. 20mm Threaded Tank Inlet (Bulkhead fitting).
You will need two of these, one to attach a tap to the tank, and another to attach an overflow pipe to the tank (if you choose to use one).
2. Brass tap or Ball Valve.
When buying a tap, make sure you pick one with the right sized outlet (the side where the water comes out, where you would connect a hose), as they come in two sizes, 3/4″ Outlet and 1” Outlet.
I believe that the standard brass garden tap size used in all states of Australia is a 3/4″ Outlet, except in NSW. For NSW use the 1″ Outlet tap.
If your tap inlet (back of tap where water comes in from) is too small and doesn’t screw straight into your Threaded Tank Inlet, you will need a Reducing Bush, which is simply a threaded plastic adapter that allows you to screw a fitting into a larger sized hole.
Reducing Bush allows you to fit a smaller tap inlet into your tank’s Threaded Inlet
You can also use ball valves in place of a tap. They are very durable, and have a ¼ turn lever, which, as you’d guess, requires only a quarter of a turn to go from fully shut to fully open. In this application you would use a 20mm ball valve.
Ball valves are much more expensive than taps, and these female-female ball valves pictured below will require additional fittings to connect them to the tank.
To connect a ball valve with a female end to the Threaded Tank Inlet you will need a Threaded Nipple, specifically a 20mmx20mm Threaded Nipple, pictured below:
You can choose any style tap, from the common brass garden taps (pictured left) to the compact 1/4 turn lever handled tap (pictured right). These are fairly cheap, and if you select the right size, it will screw straight into the Threaded Tank inlet.
Step 3 – Prepare Drilling Equipment
There are two tools that I would recommend to drill a hole into the plastic drum to fit the 20mm Threaded Tank Inlet. Either tool will do the job well enough.
1. Hole Saw.
The most recommended option, as it’s impossible to make a mistake with this one.. This is used with a cordless or regular electric drill, and leaves a slightly rougher hole that can be smoothed off with a piece of rolled up sandpaper.
To cut a hole that will be a snug fit for a 20mm Threaded Tank Inlet (which has an actual outer diameter of 25mm), you will need a 25mm Hole Saw.
2. Step Drill.
This is used with a cordless or regular electric drill, and leaves a very clean-cut hole with a smooth finish.
Since the drill is conical (cone-shaped) and the plastic of the drum is quite thick, you will need to drill the hole from both sides to get a straight through cut, otherwise the hole will be bigger on the outer side.
This is slightly more difficult to use as there is the ever-present risk of pushing the drill one step further and making the hole too large. Use only if you have experience with Step Drills in thick plastic.
The hole you will be drilling for a 20mm Threaded Tank Inlet is approximately 25mm wide, so you will need a step drill that will go larger than this. What I’ve used (pictured below) is a 10-30mm Step Drill.
Step 4 – Mark the Location of the Holes for Drilling
Next, mark the location of the hole on the plastic drum. Pick a smooth spot on the side of the tank where there are no seams or ridges, to ensure a watertight seal when you fit the Threaded Tank Inlet.
In this case I have chosen to drill the hole about 4″ (10cm) from the bottom. The reason being that if I have a tap fitted to the tank, the tap is high enough so that I can place a bucket underneath the tap, without having to support the tank too high off the ground.
Remember, the higher you mount the tap, the more water will be left at the bottom of the tank that you won’t be able to use!
Marking the location of the hole on the plastic drum
If you are fitting an overflow pipe to the tank, mark a location on the side, near the top of the plastic drum. Give some consideration as to where you place the overflow, as this will be the level when water will drain out of the tank, so the higher the better.
If the sides of the plastic drum slope in towards the top, take a moment to see how the Threaded Tank Inlet will best fit.
Step 5 – Drill Holes in Plastic Drum
Drill the hole on the spot you have marked on the plastic drum.
If you used the Hole Saw, and there are any rough edges, smooth them down with a piece of sandpaper to create a smoother surface for a better seal.
If you use a Step Drill, drill the hole bit by bit and test to see if the hole is big enough to accept the Threaded Tank Inlet. The risk with a step drill is that you can drill the hole too large! You want a snug fit!
If it nearly fits, drill a bit further from the reverse side (inside of tank) to even up the hole and test fit to see if the Threaded Tank Inlet can now fit in. Repeat procedure until you get a snug fit.
Step Drill being used to drill plastic drum
Hole drilled for ready to accept the Threaded Tank Inlet
Step 6 – Test Fit Tank Inlets
Test the size of the hole to ensure that the 20mm Threaded Tank Inlet fits in snugly.
Test fitting the Threaded Tank Inlet
Step 7 – Fit Tank Inlets
Screw the Threaded Tank Inlet into the plastic drum.
I have chosen to have the tail or shaft of the Threaded Tank Inlet extend inside the plastic drum, so I can have the fitting as short as it can be on the outside, just to save space in the walkway where I’ve located the tanks.
If you put the short side inside the tank, you’ll get more water out of the tank, and it’s easier to pour out the last bit by leaning the tank over a bit. If you mount the long side in like I’ve done here, you won’t be able to do that.
Threaded Tank Inlet fitted into plastic drum (inside view)
Threaded Tank Inlet fitted into plastic drum (outside view)
Step 8 – Tighten Tank Inlets
Tighten the Threaded Tank Inlet by using two adjustable spanners, one inside the tank and one outside.
Hold the one inside still with the handle pointing up so you can reach it, and turn the outside one to tighten it. Tighten reasonably firmly but do not over-tighten!
NOTE: You’ll need a fairly BIG adjustable spanner to fit around the 20mm Threaded Tank Inlet!
One adjustable spanner to hold the Threaded Tank Inlet inside the tank
The other adjustable spanner is used outside the tank to turn the Threaded Tank Inlet to tighten it
Step 9 – Fit Overflow
If you are just setting up a single tank, even though it’s optional, it’s best to fit an overflow outlet. This way, when the tank fills with rainwater, rather than overflowing and running on the ground, you can take the overflow and run it via a length of flexible pipe into the garden, a pond, water garden, or another container.
Tank with inlet in lid and overflow pipe on the left side
With the tap or outlet on the tank facing you, locate the overflow pipe on either the left or right side of the tank, close to the top, and on a smooth section away from any seams or ridges.
Completed overflow outlet on tank, with 22mm washing machine style flexible hose connected, running to garden
Here is a closer look at the overflow outlet, it’s identical to the outlet fitting, the only difference is that there is an 20mm elbow connected to the outside to keep the hose close to the side of the tank.
Another benefit of the elbow is that by turning it upwards, it will allow the water to reach a higher level in the tank before it flows out of the overflow pipe.
Overflow pipe mounted on the side of the tank near the top. In this picture, the end has a cap screwed on to shut it off because the overflow is not being used here, and his prevents entry of mosquitos.
If you are connecting together multiple tanks, only one tank needs an overflow pipe connected, as all the tanks fill and drain simultaneously.
The whole setup behaves as if it were one large tank, with a single inlet where the rainwater comes in, and a single overflow to let out excess water.
Step 10 – Fit Rainwater Inlet
With a single tank setup, you will need some kind of inlet where the rainwater comes in. The style of inlet you choose will partly depend on the kind of lid your plastic drum comes with, as you’ll need to adapt it for your purpose.
You must use a lid in order to prevent mosquitos breeding in the water tank. Any holes in the lid need to be screened with a fine mesh for the same reason. The fine mesh will also work as a coarse filter that prevents debris and dirt from getting into the tank.
NOTE: The lid cannot be airtight otherwise you’ll create a vacuum in the tank when you draw water from it, and the “vacuum lock” will stop the water flowing, so some kind of vent is necessary.
The lid on my tank came with a small screw top as pictured below:
I have used regular clear silicone sealer to glue a 90mm PVC Female Gutter Outlet to underside of lid.
A 90mm stainless steel mesh PVC fitting plugs straight into the 90mm PVC Female Gutter Outlet to create a filter for the rainwater tank inlet.
Different tank lids will require different solutions. Don’t be afraid to innovate and invent!
Instead of the lid, you can stretch shadecloth, flyscreen or something similar over the top of the tank and simply tie around the rim of the tank with a piece of string. The possibilities are endless!
Step 11 – Assemble Tank Stand
Construct a tank stand out of concrete blocks (Besser blocks). Place two side by side so they are wide enough apart to support as much of the tank base as possible.
Two concrete blocks used to elevate the tank
Place two standard rectangular pavers across the top of the concrete block to complete the tank base.
Tank base made of two concrete blocks (Besser blocks) with two concrete pavers laid across them
Step 12 – Position Tank
Position the tank on top of the base.
Important – make sure that as much as possible of the bottom edge of the plastic drum is sitting on top of the pavers. The simplest way to do this is to position the base and the pavers so that the edges of the pavers stick out past the bottom of the tank.
(The rest of the bottom of the plastic drum is not critical, the edges supports all the weight, and a full drum of water weighs 220kg!)
Tank located on base, note that the edges of the pavers extend beyond the base of the tank
Step 13 – Install Fittings
If you are just setting up a single tank on its own, fit the tap to the tank at this stage.
Take your tap and wind around the threads with Teflon plumbers tape to create a watertight seal (see instructions below), and then screw it by hand into the Threaded Tank Inlet. Hand-tighten only.
Install any fittings require to connect a pipe to the overflow outlet, and use Teflon tape on any threaded (screwed in) joins.
The water tank should now be complete and ready to use!
Handy Tip: Using Teflon Tape on Threaded Plumbing Joins
A few tips with using Teflon plumbers tape:
Begin wrapping the threads from the end and wind down.the length of the fitting or pipe (as shown in picture).Wrap in the direction of the threads. Wrapping the wrong way may result in the tape coming unwound as the fittings are tightened.The simplest way to describe this technique is with a few steps for a right handed person.Hold the pipe or fitting in your left hand with the end facing you (just like the pipe in the picture)Holding the roll of tape so it looks like a “snail”, with the tape unrolling off the bottom edge (as pictured), wind it on clockwise with a little bit of tension, for around 7 turns.
You wind the tape clockwise so it stays on when you screw the fitting in, if you wind it the other way it will unwind when you screw it in.
You hold it “snail-wise” with the tape feeding from the bottom so you can tension the tape as you wind it. If you hold it the other way the tape loops out faster than you can wind it and it’s impossible to tighten it as you wind it!
Connecting Multiple Tanks Together & Additional Tank Enhancements
The tank I have assembled in this set of instructions is to be connected to 5 other ones I have previously set up, so I’ll just be adding a connector to plumb it in to the main supply line of the pump.
Instead of fitting a tap, I’ll use a 25mm x 20mm Threaded Reducing Nipple to connect it to the main supply line of the pump
25mm x 20mm Threaded Reducing Nipple
Step 1 – Prepare Fitting
On the smaller end of the 25mm x 20mm Threaded Reducing Nipple, wind around the threads with Teflon plumbers tape to create a watertight seal.
Step 2 – Attach Fitting
Screw the 25mm x 20mm Threaded Reducing Nipple into the Threaded Tank Inlet and tighten with an adjustable spanner. You won’t need to over-tighten the fitting because the Teflon plumbers tape will create a fairly tight seal with only a moderate amount of tightening.
25mm x 20mm Threaded Reducing Nipple screwed into the Threaded Tank Inlet
At this point I will explain some of the design of the multiple tank setup and the rationale as to why I’ve used the fittings that I have. feel free to skip this section if you so choose to!
The pipe that connects the tanks together is cheap 19mm black irrigation poly pipe. This is adequate to join all the tanks together and works reasonably well as a “balance pipe” which allows all the tanks to fill, and drain, at the same time.
If you use the smaller 13mm irrigation poly pipe, it is far too small and the flow is drastically reduced, so in a heavy downpour, your main collector tank (where the rain water flows into) will overflow because the thin pipe cannot fill the other tanks fast enough.
The bigger the pipe diameter the better, but if you use 25mm irrigation poly pipe, you have to use larger size fitting, and the cost of the larger size fittings starts to become prohibitively expensive, especially with multiple tanks!
So, using a 19mm irrigation poly pipe is the optimum size between cost and performance. When plumbing any pipes to supply water, you ideally want to keep the size of the pipe the same size, as using any fitting that narrower than the pipe size restricts the flow of water.
So what does this mean? If you’re using a pump with your tanks, the pump won’t be able to pump as much water, so you won’t be able to pump it as far, or the lengths of irrigation pipe/number of irrigation points that your pumping to, will be reduced. So it’s critical to not restrict the supply pipes!
So what does this mean for our project? Basically, you want to keep the inner diameter (the “hole size”) of any fitting at around 19mm. We’re using 19mm irrigation poly pipe, and a 20mm Threaded Tank Inlet. If we are going to connect anything to this we want to keep the internal pipe diameter the same.
To connect a 20mm Threaded Tank Inlet to a 19mm irrigation pipe, we can use a single fitting, a 19mm tail x 20mm BSP male director, pictured below.
The downside is that we cannot easily disconnect the tank by hand if we need to.
We can use a fitting called a Nut and Tail instead, pictured below:
A Nut and Tail can be turned by had to screw and unscrew it from the tank. It has a rubber washer in it to create a nice tight seal with minimum pressure. This is rather handy as you don’t need any tools to remove a tank.
To connect the Nut and Tail fitting to the tank, you need an adapter which has male threads on either side, this fitting is called a Threaded Nipple, pictured below:
During the design process, I figured that since the Nut and Tail is hand tightened, it would be easier if the “nut” part was a bit bigger to get a better grip on. This is easily achieved at no extra cost.
Instead of using a 20mmx20mm Threaded Nipple to join the Nut and Tail to the tank, we can use a 20mmx25mm Threaded Nipple. It’s actually called a 25mm x 20mm Threaded Reducing Nipple (pictured below), but we’re using it the other way round to “expand” the size of the connection.
If we use a larger Nut and Tail, a 25mm BSP Nut x 19mm tail, the “nut” part is larger, so we get a bigger grip, which is easier to turn.
I hope that was not too confusing and explained my reasoning for this aspect of the design!
Step 3 – Construct Adapter to Connect Tank to Other Tanks
The adapter is made from a 19mm barbed T-piece, or T-joiner (pictured left), a short length of 19mm irrigation poly pipe and a 25mm BSP Nut x 19mm tail (pictured right).
Fit the Nut and Tail to the T-piece, the assembled adapter shown below:
Step 4 – Fit Adapter to Tank and Balance Pipe
Screw the adapter onto the tank, hand tighten, and push fit the balance pipe (which connects all tanks together) into one end of the T-joiner.
Adapter connected to new tank and balance pipe
Step 5 – Optional – Fit Siphon Pipe to Tank
This step is optional, but it’s one innovation that I invented that’s worth it’s weight in gold if you are using a pump. If you’re not using a pump, you might want to skip this step, thought it still has some benefits even when you just fit a tap to the tank.
One of the problems with having the outlet on the side of the tank is that you always end up with water below the outlet that you can’t get to, so it just sits there. No big deal with one tank perhaps, it may be just 20 litres. But when you have multiple tanks, this unusable residual amount adds up. With a six-tank setup like mine, that adds up to around 120 litres, which is equivalent to a half of a single tank!
The simple solution is to connect a 20mm elbow to the Threaded Tank Inlet inside the tank, then screw in a short 20mm riser tube and push the end of the tube down so it touches the bottom of the tank, as shown in the picture below.
With a pump connected, it works just like drinking with a straw, it sucks every last bit out of the bottom of the tank.
Step 6 – Connect Tank Adapter to Pump
Connect the other side of the T-piece to a short length of 19mm irrigation poly pipe, and connect an inline 19mm tap , then run the other side of the tap to the pump.
Balance pipe connected to tank, terminated with an inline tap, and connected to pump inlet hose
Step 7 – Set up Pump
This is my pump set-up. The white pump inlet hose is connected to a filter (bottom left) to remove any particles from the water, in order to prevent wear on the pump, and to prevent clogging in the “drip-line” irrigation system.
The green hose is the pump outlet. This pump has a “manometer switch”, the big yellow cylinder at the top – it’s a pressure activated switch, it switches the pump on when you try to draw water, and switches off automatically when you stop. It all sits on a raised concrete plinth to keep the pump out of dirt and water on the ground.
Step 8 – Connect Pump to Tap
This is the complete pump setup. The plastic pump cover protects the pump from rain and sunlight. The pump is connected to an outdoor waterproof power inlet. The green outlet hose is connected to a tap mounted on the wall.
As the pump has a pressure activated switch, when you turn on the tap, it turn off the pump, and water runs, when you turn off the tap, it switches the pump off.
This system allows me to use the tap in the same way as the taps on the mains supply, the only difference is that this tap supplies rainwater from the tanks. Just like the mains water taps, I can connect a hose to it, fill buckets or watering cans, it works identically.
A closer look at the tap setup. I’ve chosen to use regular garden hose “click-fittings” for convenience to connect the pump to the bottom of the tap, and to connect things to the tap. I’ve drilled into the brickwork to secure the tap firmly, and used plastic plugs with screws to fasten it in place.
Well, that’s the whole design, from the recycled drum to the fitted tap, and everything in between. Your setup doesn’t have to be this fancy to collect rainwater. A bare plastic drum or old wheelie bin under a broken gutter pipe will collect rainwater so too. All the fittings, pumps, etc. are all about convenience. Simply do what you can, start simple if that helps, and then experiment to see if you can do things better.
My first attempt at rainwater harvesting was with a converted wheelie bin that sat under a cut off gutter pipe, and guess what, it worked great! And if you’re wondering, here it is, and I still use it!
I’ll post the design for this wheelie bin water tank soon!
In the meantime, get out there and harvest all that free rainwater that nature bestows us with, and make a difference, every little bit counts!