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Efficient Water Usage and Storage
Last updated 11:46 am, Friday 13th November 2009

Why be efficient in your water usage?

Good question! This all really comes down to the cost (in all senses) in the provision and maintenance of the water supply infrastructure. The better and more efficient you are a consumer of water, the less demand you are placing on the water supply infrastructure and ultimately on the environment and the local ecology. Also if the water demand as a group is reduced, the individual cost to the consumer should be less, so you are also saving yourself money in the long run.

Being water efficient

Efficient Water use is actually a three stage process:
  • First, you need to collect the water in an efficient manner (i.e. get the most/best water you can)
  • Second, you need to store the water in an efficient manner (i.e. least cost and most reliable to guarantee continued water quality),and
  • Third, distribute and use the water in the most efficient manner (i.e. when to use and how to use it).
Each of these stages in their own, if done right, will bring water efficiency benefits; but you will get a sort of 'multiplier effect' if you do all three right. Now onto the finer details...

Efficient Water Collection

Unless you happen to live on a boat in a fresh water lake, collecting clean water is going to require some infrastructure development. 'Traditionally' there are 3 main ways to collect water:
  • From suitable roofs
  • From suitable bores
  • From someone else..
The 'someone else' option is usually in the form of a 'pipe' from either a state water supplier or someone close to you who has excess water. With this option it is very likely you will pay according to consumption, depending upon the supplier this could either be very ecological or not very ecological at all (thinking Sydney here). This is good as a backup but you should not be dependent upon it for your day to day water usage, especially with the predicted price increases coming through.

Bore hole water collection

Bore holes can give you access to a large amount of water. Although do be very careful with this, as firstly the quality of the water you 'pull' might not be all it is claimed to be, and secondly you might be paying through electrical pump costs to 'pull' the water. Also if your neighbors are doing the same, that increases the demand on the water, which could make the water recede and you end up with a dry bore! Also pulling water from the bore could effect the ground water level, so damaging the environment else where (drying up rivers, etc)

Roof Rain water collection

Roof rainwater collection is perhaps the most environmentally friendly (or least damaging) way to harvest water. It has several distinct advantages:
  • The water by volume is 'free', i.e. you don't pay per mega litre, etc;
  • The water, assuming a clean roof and infrastructure, can be clean enough to drink! (where do you think the water in your tap actually comes from?)
  • Given the 'sudden downpour' nature of most rain events where I live, the impact of you harvesting rainwater is quite minimal as its literally 'washed out' compared to amount of water just falling to ground. Also when your tanks are full they will overflow to ground as well. Just think of it as borrowing the rainwater to later put back into the natural system at your deciding

The Roof

So how do you go about this collection from the roof? Firstly; assess which 'planes' of your roof are worth collecting from. Some roof planes may be heavily overshadowed by trees so would collect a lot of leaf litter (check the gutters), this taints the water. You can put on leaf guards on the gutter, but in some cases the benefit would be marginal. Also do a cost/benefit analysis on the smaller/harder to reach roof planes; they may not be worth the plumbing effort to harvest. I have one roof plane on my Cabana that was the wrong side to the tank with not enough fall and it was overshadowed by trees, so I left it out.

Next, work out what the square meterage is that you are collecting from as a 'flat' vertical view. i.e. a roof at 45 degrees will not collect the same as a roof at 20 degrees. Use your house plans for this and just measure straight off the plan, do not climb your roof to get these figures! Round down to the nearest square meter.

Next, try and find details of what the mean annual rainfall is for your area in millimeters. BOM and some local councils will be able to point you in the right direction for this; try their environmental departments.

Next, multiply the square meters by the millimeters of rainfall you have (i.e. 35 sqm x 20 mm = 700) - this figure is your total harvested LITRES of water per year during an average year - should be quite a bit for a large roof!

Next, work out the water consumption you can 'attribute' to the harvested water; i.e. don't count drinking and cooking water if you are on mains supply. Charts like this abound across the internet, plus several interactive calculators. You are aiming to end up with a total harvested water usage figure for the year. Also make good use of your water utility bills if you have them.

Okay so far? Now subtract the total harvested water figure from the harvested water usage figure - if the result is negative, this indicates that for some part of the year there is a good chance you will need to use other water sources (i.e. mains or bore) to 'top' you up. If its positive, there is a good chance (given big enough storage) you won't need topping up.

Check your gutters (Australia)...

If your house has had new gutters put on it in the last 10 years, do check to make sure that they are not the 'high front' variety?  i.e. the front of the gutter is higher than the back of the gutter facing the wall. Why? Well, this particular style of gutter has been rather popular as it looks attractive and is cheap to install, but the downside is that in a heavy rain downpour, when the water volume is such that the gutter down pipes backup, the water will find its way out by the next lowest point, which will be the back of the gutter directly mounted onto the wall! The big negative with this is that either the outside wall is made wet, or if the gutter is mounted right to the top of the wall (as it is on most modern houses), it will flow inside into the wall cavity and make that nice and wet.. This will lead to rot, termites and the possible structural failure of your property!... You have be warned, so do check!

How big is your water tank?

So how do you 'size' your water 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 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!

What type of water tank?

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

Buried in 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...

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.

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 upto 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, thats 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 opto for doing without the trouble in the first instance!

Where to put your water tank?

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!

Keeping your water clean..

An important part of the rain water process is trying to avoid leaves and other 'undesirables' getting into your tank water. Look at the following:
  • First flush diverters - these work, although they do require you to clean out the mechanism on a regular basis (i.e. twice a month); otherwise the filters just clog and you end up with dirty water just standing in the diverter..
  • Slow water traps - basically an inline section of pipe bigger than the input pipe in a U bend configuration with an access hatch at the bottom. Idea is the water slows up through this section and the heavy stuff sinks to the bottom to be later removed via the access hatch.
  • Gutter leaf guards - simple and effective. Bunnings sells a self fit mesh for about $10 a roll. Just remember to make sure you pull it flush to the roof line in the gutter, i.e. no gap behind it for leaves to accumulate and rot in. If you are replacing the whole gutter look at SmartFlo.
  • Water tank 'flush' outlets - this is where either the overflow mechanism in the tank is linked to a pipe running along the bottom of the tank, so the force of overflow 'hovers' out the dirt at the bottom of the tank. The other form is a simple bottom outlet to dump the dirty water at the bottom.
  • Water tank entrance filters - quite common these, but make sure to check them once a month and clean out the rubbish. Also make sure to keep the cover on them, or the light that gets through the filter could start growing 'things' in your tank.
  • Water overflow 'gates' - these are simple spring loaded flaps to stop wildlife going up the pipe and nesting in your tank.

Efficient Water Use

Now that you have gone to all this trouble of collecting water, you need to ensure you get the best benefit from it.
Water so collected can be used in the home in the following places:
  • Toilet flushing, and,
  • Washing clothes
This may not sound like a lot, but these two uses can account for up to 70% of typical water usage if combined with garden watering..
Now add onto this the following cases:
  • Washing the car, and,
  • Topping up your pool
You can get up to 85% water usage from your tank, i.e. only 15% of your water usage comes from the mains.

Watering plants

Assuming you have a tank and you want to water your plants from it, you need to do the following:
  • Buy and install an irrigation timer with a battery backup and 6 zones - why 6 zones? This means you can set up 6 different types of watering 'types' in your garden - which should cover all types of plants. Also make sure its also wired up to a rain sensor - no point watering after a good shower.
  • Put in place a drop irrigation system for permanent plants - this can go under the mulch..
  • Always mulch! - evaporation due to the surface heat will rob your plants of upward of 60% of the water you give them without mulch! With mulch the water 'hangs around' longer - so you will not need to water so often to maintain the plants.
  • Make sure your soil is not 'aquaphobic', i.e. does not absorb water - you may need to add more organic matter. Easy test for this just put some of the soil on a surface, make a small well in it and put some water in that well - if the water just sits there, in a bubble, you have soil aquaphobia. Note: there all sorts of 'fancy' treatments for this, but you really need to get the basic quality of your soil up to really overcome it in the long term.
  • Always water in the evening (i.e. after 4pm in most places) as evaporation will be less. Also, if watering around the house in summer, you will get some benefit in cooling from the evaporation that will occur. Also house plants are good to have for similar reasons.

More efficient water use, to even not using any!

May seem a strange thing to mention - but if you really are keen to cut back on using your water, or do not have much water to spare, there are some alternatives..

Related Tags: water, rainwater, water tanks, gardening

Related Listings: Rain Water Harvesting, Rain Water Tanks, Gardening, Home & Garden

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