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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.

Related Tags: water, rainwater, water tanks, gardening

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

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