Aug 10, 2016 11:04 am
We are installing a water tank as we will be living rurally and it just makes sense. But I have no idea how big or how many to get. We will have town water hopefully but I know that many people in the area wont drink it, only using it for showers and washing. We have a 3 person household. I have a 5000L tank in mind. How long will this last us? Would we need two?
Re: How much water do we need?3
Aug 10, 2016 12:04 pm
Oh really? It will be in Boorowra, NSW. I was more hoping to know how much water the household would use a day so I can work out how much we would need but then I have to factor in rain fall too. I tried googling but got nothing
Re: How much water do we need?4
Aug 10, 2016 1:28 pm
Google "water tank calculator". There's plenty around, some more in depth than others. Tankulator is one.
They'll determine two main things.
Firstly, the water volume you'll receive for storage. Calculated by determining your catchment area (your roof area), & the average annual rainfall at Boorowa.
Plus your water usage. Can't find it from a water bill? If not, some of the calculators will help, if you know flow rates & times for things like showers & sprinklers. Plus in household size, other water use etc.
Looks like you receive around 600mm of rain a year, around half of what Sydney receives. Doubt you'd cover all your water use, unless you low water usage, or have a large catchment area. But you could certainly cut down your mains water usage substantially.
Re: How much water do we need?5
Aug 10, 2016 1:38 pm
Here is the quick calculation I did for our future build a year ago.
and look to the pages on rainwater tanks for calculations
Calculating rainfall and tank size
Using data from here... http://www.bom.gov.au/climate/data/
and selecting weather stations from here...
ftp://ftp.bom.gov.au/anon2/home/ncc/met ... SW_139.txt
Now you need to measure the roof horizontal area that will be drained to the tank/s in m2. Depending on the roof shape it may not be practical to drain the whole roof to a single tank.
Multiply the area m2 by the rainfall in mm for each month and divide by 1,000 will give you the volume of rain in kilolitres
Area of proposed roof ( Rev 15 ) = 210 sq m
Site Name Lat Long
066153 MANLY VALE (MANLY DAM) -33.7822 151.2556 Jun 1906 Oct 2006 50.8 50 N
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual
Mean 115.9 113.8 126.3 138.6 119.7 102.6 98.4 72.7 70.9 73.1 86.0 85.9 1225.6
kL ave 21.1 --> 21.1
Average rainfall = 1225kl per year so each month averages out to approx 100kl
So Rev 15 roof of 210 sq m can hope to collect each month 21.1 kilolitres of rainwater
As a comparison; if you can keep to the water boards Target 155L per person per day that is the equivalent of 57kLper person per year.
155L x 30 days = 4650L per person per month
3 people should consume 13950L per month
Going by the last three water bills we consume approx 20,000L per month
We are installing a water tank of around 20,000L which should be more than adequate for laundry, toilets, garden etc
Re: How much water do we need?6
Aug 13, 2016 2:44 pm
Good posts by ddarroch and Stewie D.
Before answering how long your water would last, we need to know the total sq m of your roof catchment areas and whether all roof areas would be harvested.
The ATA Tankulator uses a yield factor of 80% from memory. Yield is variable and first flush diverters can kill yield. 65% is not uncommon.
The system has to be set up correctly but very few are. There are a number of posts in this sub forum that mention common sub standard practices to avoid and simple methods to improve common practices and water quality.
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