> The facts about Water Tanks

The facts about Water Tanks
Last updated 8:54 am, Tuesday 23rd May 2017

Water tanks, what are they used for?

Water tanks usually have five main uses:
  • water for the garden - basically water to do plant watering with, so conserving water and saving you needing to use mains water;
  • water for fire fighting - very Australian, but an important usage none the less;
  • water for drinking - rain water if stored in the correct tank is quite suitable for drinking;
  • water for washing - you can easily use this water for washing your clothes in, and;
  • water for flushing the toilet - perfect for the job!

How big does the water storage tank need to be?

Given the above usage cases; how do you 'size' your water storage tank? The trick here is to have enough storage to 'carry you through' the periods of no rain given sufficient prior rain. The above positive/negative figure will give you a steer on how likely being able to carry through will be, the more positive the easier with adequate storage; the more negative the less worthwhile as a goal this is (so don't bother getting such a big rain water tank).

The size you need also depends a lot on your rain fall patterns - if you have well defined periods of the year that are 'wet' and 'dry' then you should aim to collect as much as possible to carry across into the dry periods. If its more random and equally distributed across the year, then you just need to hold enough to 'flatten out' the random distribution (i.e. a quarter of a years total rainwater would be more than adequate). Your consumption of the water also comes into play, if you consume it all before it can be saved over the medium term, a large tank will spend most of its life empty!

Although, from talking to many people on this issue, I always hear the same story; namely 'I wish I had got a larger tank'. I think this is more down to the changing weather patterns which have condensed what was previously a months worth of rain into a day!

NEW - we have just completed an online Rainwater harvesting calculator that you can use with you real monthly rainfall figures and your average water consumption information to get exactly the size of rainwater tank you need.

Water tank type?

Water tanks come on many different types, shapes, sizes and colours; but can be grouped by final insulation location, as follows:

Tanks buried in the ground

These are either plastic or concrete. Plastic water tanks will be supplied as a whole unit that is 'dropped' into the hole and filled over. Concrete water tanks require form work, pouring, topping off and covering over. Plastic is in essence quick and easy, concrete slower but more 'solid' - i.e. should last a lot longer.
Where it is viable to bury your tank is determined mostly by your budget and the ease with which the required hole can be made. Also be aware of ground water on the site, if this pools in the hole, you can end up with the empty tank literally 'floating' out of the hole...

Tanks under the house

Unless you are building a new house, your only real option here is what are known as 'bladder water tanks' - in effect a big rubber bladder that rests in a special frame in the void space under your house. Big plus is that you don't have to dig holes or take up yard space with a water tank. Downside is that the capacity is usually limited and you pay a premium.

Tanks above ground

This is where you will find by far the biggest variety. Everyone and his wife is either making or selling some form of above ground water tank. The trick here is to use the right 'type' of tank for the size and expected life.

Above ground small plastic water tanks - These go up to around 2000 litres and come in all manner of shapes: round, square, cylinders, etc. They are mostly designed for use on the smaller plot where finding somewhere to 'fit in' the tank can be hard. Often they end up mounted on a small stand. Big downside with these is the lack of water storage and the fact UV will degrade the plastic - so fixed life span (or keep them out the sun and/or paint them).

Above ground big plastic water tanks - These usually go up to 15k litres and are shipped to site whole and ideally 'dropped' right onto a special sand based pad that becomes their home. The big plus here is that its ready to go. The big negatives is that they don't do well in a bush fire and the UV will degrade the plastic over time - so have fixed lifespan. See Nylex Water Solutions for tanks of this type.

Above ground metal water tanks - Basically a big metal 'water butt' with some internal treatments to reduce corrosion effects. These can go up to 150k litres typically. Cheap but the fact the metal is performing two roles (structural and water lining) means they are susceptible to failure due to movement - so they are often mounted on frames or towers as part of the package. Also rusting puts a limited life on them.

Above ground concrete water tanks - Basically a big reinforced concrete box or cylinder. These go up to the millions of litres with a cost to match to boot. No problems with rusting, although be careful on settlement as it could crack the tank. Also no way to move it once its in place, so be darn sure you wanted it there.

Above ground metal water tanks with plastic liner - Think of this as the 'bladder tank' going outdoors. The metal provides the enclosing framework, whilst the liner does the job of keeping the water in. Big win here is that settlement won't loose you water, and rusting doesn't make the tank leak. Sizes up to millions of litres. See Pioneer Water Tanks for more details. Another plus is that the liner is often 'food grade' - so good to drink from direct.

Is it all worth doing??

A whole load of factors come into this: some you can quantify, some down to a lifestyle choice.. The simple factual information is best worked out over the expected lifetime of the various solutions you have available. i.e. look at things over 10 years at least. Most good water tanks should still be functioning well after 10 years with a little bit of TLC. So work out the amount of water 'saved' by the water tank compared to say mains water, i.e. the cost of the tank water if you had it from the mains. Subtract from that the actual full cost of the water tank and you get the nominal cost now amount (no depreciation or price adjustments) you will save (positive) or loose (negative) from utilizing a water tank over 10 years..
Then to that figure add on the cost of replacing any items you will 'loose' or be unable to support without the mostly guaranteed supply of the water tank. i.e. think expensive none drought tolerant plants (and veggies). Difficult to work out precisely but for some people this could be a rather expensive replacement cost.

Another factor to consider, that is very Australian, is that in bush fire prone areas having a large water tank with the right attachments can help the fire services in fighting fires - so reducing the potential risk of fire damage to your property by proxy... In theory your insurance should cover you, but I'd opt for doing without the trouble in the first instance!

Where to put the water tank?

By now you should have an ideal figure for the amount of water you need to store, so next you need to think about where to put it... Remember 1000 litres takes up 1 cubic meter (no getting away from that, its physics!). Also remember most tanks come in height multiples of around a meter (plus 50 cms for the top). Also councils have weird and wonderful restrictions about where the tank can go (think boundary and overshadowing). Plus if its over 10k litre it will usually have to be covered under some form of planning permission.. So think about this hard. Also you can have more than one tank easily enough and that might be cheaper than digging out a massive hole. Also remember when you take the water 'out' of the tank you want its water pressure to be of use to you if at all possible, i.e. put a tank high on your plot under the 'highest' roof, so you can water your garden using just gravity and no pump!

What about the run-off?

No matter which water tank you decide to put in - as soon as it fills up the excess water will come out of an 'overflow' pipe. Now for a small tank and feed-in this is not that much of an issue; but if your tank is feeding off more than about 200m2 of roof area you could end up with quite a volume of water flowing out of that overflow.

Such a volume of water can result in significant localized flooding and erosion on its own, so it pays to 'manage' this water up front using the following techniques.
  • Discharge the water into a 'swale' system - this is a set of humps and curves made in a gentle slope to slow the water down and encourage it to settle into the soil instead of running straight off your land.
  • Install an overflow 'weir' basically a normal flow of overflow water just goes into the swale system, but a very high amount goes over the weir and then into a storm-water pipe to carry it away into the storm-water system directly rather than overland. This weir is easy to make with some stone and pipe fittings.
  • Get another tank... Seriously, if you have the land space and can 'chain' together tanks in this way you will maximize the amount of water you capture. For instance on our plot we have a tank on the high side whose overflow is plumbed into the rainwater capture for the lower tank which feeds off the house roof. The overflow of that then goes off across the lower paddock and around the chicken coup to the creek.

Related Articles

Related Tags: water, water tank, rainwater, rain

Related Listings: Rain Water Harvesting, Rain Water Tanks

The facts about Water Tanks
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Comments left

  • Water Tanks said:

    Drinking Water is becoming one of the most rare goods in the 21st century. and to save water we do installing a water tank in the house is going to enhance the property value as shortage of water is a coming problem and we have to solve this.

    ON Thu, 26 Aug 10, 9:55am probably from India  Reply to this comment

  • Rainwater Tanks said:

    These are really very amazing facts about water tanks and are becoming popular and are also useful to save the water.

    ON Thu, 30 Sep 10, 6:54am probably from Australia  Reply to this comment

  • Suzquestion said:

    We are in the process of buying a home that has a water tank in the basement that collects the ground water from the sump pump to feed the sprinkler system. Are you familiar with this type of system? Should we be concerned with this in our basement?

    ON Fri, 15 Oct 10, 7:50pm probably from United States  Reply to this comment

  • Carmen said:


    We live in South Africa on a farm with our own bore hole. We are thinking of installing a water tank to collect the rainwater for use. What i am wondering is, if the water stand still in a tank for 5 - 6 months before usage, how does that affect the quality of the water (algae etc?).

    ON Mon, 9 May 11, 6:58am probably from Australia  Reply to this comment

    • Eco Guy said:

      Your water will only degrade if light can get into the tank, without light nothing will grow in it - think about water in a pipe, apart from the surface of the water in the tank, its the same situation.

      ON Fri, 2 Dec 11, 12:18am probably from United States  Reply to this comment

  • William said:

    Hi there, we are building a new house, there are three old above ground big plastic tanks. Should I keep them for future use. How do I clean the inside.? The main use of these tanks is for watering gardens. Thanks!

    ON Thu, 1 Dec 11, 12:08pm probably from Australia  Reply to this comment

    • Eco Guy said:

      Hi William,

      If they are in a good state of repair - keep them. As for cleaning, if you have a filter on the input and a 'first flush' divert in place, the amount of crud on the bottom would be quite small. Cleaning it is probably a professional job, depends on the size of tank and if you want to flush out all the water as well. Some tanks have a bottom flush device..

      A good tip is to actually paint the outside of the tank, this freshens it up and helps protect it from UV damage - looks like new and far cheaper than buying more tanks.

      ON Fri, 2 Dec 11, 12:16am probably from United States  Reply to this comment

  • Salah Ud Din said:

    I want to know that whcih type of elevated water tanks are suitable Either circular shape or rectangular shape? It is to remember that I want to construct RCC water tank? Please inform me through arshadlashari17@yahoo.com

    ON Sat, 11 Feb 12, 5:16am probably from Afghanistan  Reply to this comment

  • Jenny Lin said:

    What are some negative things of owning a water tank? there has to be something

    ON Thu, 23 Feb 12, 10:13am probably from Australia  Reply to this comment

  • Kim said:

    I need to paint a mural on a 8 ft by 4 ft. water tank. I am not sure what type of paint to buy for this it will be in the sun. Please help advise.

    ON Tue, 15 May 12, 4:17am probably from United States  Reply to this comment

  • Suzel Cafrine said:

    encountering acumulation of jelly-like sedimentation in a galaxy water storage tank three months after installation. one with aqualiner water storage liner. what is the cause? we have been getting desalination water

    ON Fri, 10 May 13, 9:17am probably from Seychelles  Reply to this comment

  • Rainwater Tank said:

    I agree with the points mentioned here! Water Storage tanks can be used to accumulate the water for future purposes. The lined tanks are much effective than the normal ones.

    ON Wed, 5 Jun 13, 2:25pm probably from India  Reply to this comment

  • Sheetal Patidar said:

    Can I make a cube shape tank with concrete,bricks and cement of size 100×100×40 foot. My purpose it for irrigation. Please tell me about technical issue and roughly cost for the same.

    ON Wed, 4 Sep 13, 4:34am probably from India  Reply to this comment

  • Angie said:

    Hi. We are a kindergarten in VIC , We use tank water on our gardens and let the children use it for sand play NOT drinking. Are there any health concerns involved? Thank you

    ON Wed, 8 Oct 14, 2:51am probably from Australia  Reply to this comment

  • Gheith said:

    Have you heared about Castagra one of the best and safe coating material . Regards Dr.Gheith

    ON Wed, 6 Jan 16, 4:54am probably from United States  Reply to this comment

  • Victor said:

    i am considering installing two water tanks one for waste water from shower bath basin that will be treated and used to water the grass and garden, and the second to collect rain water for drinking. i was unsure on what size tank i would need to buy but your article helped a great deal thank you.

    ON Wed, 20 Jan 16, 2:13pm probably from Australia  Reply to this comment

  • Tom Toberty said:

    Hello, I am about to purchase 2 X 26,000ltr used plastic tanks with their pump and piping. They had been used for about 30 years until they were allowed to run dry 7 years ago. Could this cause a problem with the tanks, or the pump and pipes. Thank you.

    ON Mon, 21 Mar 16, 6:58am probably from Australia  Reply to this comment

  • Daniel Wyatt said:

    Hello, The link to Pioneer Water Tanks in the section on "Above ground metal water tanks with plastic liner" isn't working. The correct email address for the link is www.pioneerwatertanks.com.au Thanks

    ON Fri, 20 May 16, 12:51am probably from Australia  Reply to this comment

  • Shammy Peterson said:

    You made a good point when you said that size of the water tank will depend on your rainfall patterns. My husband and I are interested in having a concrete underground water tank installed next month so we would have a source of water during emergencies. We will be sure to speak with a professional to get help in determining the size that we need since we want to prepare our budget.

    ON Tue, 26 Oct 21, 9:42pm probably from Norway  Reply to this comment

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