There are a lot of issues here but here is an overview.
A 20,000 litre storage is very small when you are talking about a total house supply. Your harvest area may also appear large but don't be mislead by various web site claims that 1 sq m X 1mm of rain = 1 litre. Rain harvesting IS NOT 100% efficient, it is closer to 85% maximum but usually a lot less. This reduces every 100mm of rain on 280 sq m from 28,000 litres to 23,800 litres maximum. An average year's rainfall would supply an average targeted use (150 litres per person per day) 2 person Melbourne household but no more unless you had a wet year.
You mention supplying the entire house but also mention a mains back up supply. If you have a mains water supply passing the property, you will be charged service fees regardless of whether you use the water or not. You also cannot cross connect the mains supply with a water supply collected onsite unless you have plumbed a number of provisions to prevent back flow. This is why tanks connected to a laundry for example are plumbed to a third tap. There are also a number of other regulations to consider, plumbing, Vic Health etc and you need to know what these are before you decide on what you would like to do.
Mains back up devices are expensive and why would you want to partially refill a tank with water delivered under mains pressure to then use a pump to supply the house? Some back up devices also use some mains water to prime the pump every time the pump is used.
The submersible pump will have a float sensor that cuts the motor if the level drops and you can also have a separate tank level sensor fitted. Some people even wire the level monitor to their PC!
There are too many issues to go into here but perhaps you could consider supplying only the toilet(s), laundry, hot water service and an outside tap.
Under ground tanks and bladder tanks in particular need very good prior filtration and a lot of systems that have stagnated have been difficult to clean. If you have a truly professional installation and a good pre and post tank filtration system, you will have top quality potable water. A first flush diverter on its own just doesn't cut it.
Potable consumption is only a few litres per day and you could have this by keeping a jug (filled from the laundry) in the fridge. Filtration can be by a 2 stage cartridge and UV system for optimal results. There is plenty of info online.
Posted Wednesday 14 Dec 2011 @ 10:39:07 pm from IP
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