Running a washing machine with "grey" water is a none starter, yes it can be done provided you get either the pressure correct in the height between the outlet on the water butt and the washing machine intake so unless you are able to raise the water butt by 10 metres I very much doubt it will work.
Then there is the much more important and essential element that you will require, the ability to almost purify the water and turn "grey" water into clean drinkable water.
This is not cheap and the average washing machine running an average 4 member households worth of water uses between 12000 - 15000 litres per year, notwithstanding the shear cost in filtration alone plus the fact you would be required to install either a large height butt in the region of 10 metres to get the head of water or a pump to ensure a 1 bar pressure then the energy put into the system would far exceed any potential savings.
I agree and have done so with 2 of my water butt's, 1 feeds a downstairs toilet via a carbon filtration system and the other 250 litre unit is used to either top up the smaller one if required or water the garden Nd jet wash the car again having a carbon filtration system installed which requires changing in the set up I have every 8 -10 months so very energy efficient and due to swapping onto a water metre the home I live in I now pay around £25 per month, now this may not seem like much but when you compare the pre installation of my system and going onto a water metre I was paying back in 2006 a little over £1000 per year.
So even with the small costs of maintaining the fters every 8-10 months (homemade by the way, just do some research and you can nip out to your local beesley & fildes or B&Q and obtain the required substrates to make the carbon filters, very easy and apparently can turn a bacteria ridden pint of water into drinkable (although I wouldn't risk trying)!
In summary water butt's can work extremely well if used core try and piped up well, combined with some of the latest solar panels and a bank of leisure batteries you have yourself a set up that can sustain you for a few days of grid.
It's amazing how these things are not mandatory for new builds considering the government's stance on carbon neutral footprints etc. I estimate my whole set up costs no more than £150 to install (water side only) and then about £20 a year on average rebuking the carbon filters home made of course.
There is also the fact that if you have any WC unit which has an accessible lid if you fill a 1.5 litre bottle of water with salt water it will happily sit on the bottom of your system and for EVERY FLUSH save you 1.5 litres without compromising on performance so add that all up 6 over a year the average 6 litre WC is flushed 10 times per day, that's a saving of 5475 litres per WC!!!
It really is a no brained and as stated with my solar set up with old leisure batteries when I come across one it gets added to the bank and when wired in a particular way with a power inverter then you can run a house for days off grid no problem.
The set up costs of solar are still high but my £900 set up is enough to save me a lot and over a 2 year period it's paid for itself and now provides free power!, don't get roped into the government-funded schemes they are all rip offs, source your panels from China and most other electronics plus all the advice you would need to set it up from the likes of Maplin or a similar electronics store.
I have saved literally thousands, give or take £7k over 5 years and given the set up costs and equipment it's still £5-6k plus
Go carbon neutral and you'll never go back!!
For a small fee I could install the equipment for you, I would charge about £120 a day and it's a 2 day job plus the set up costs of £6-7k depending on what type of set up you want you could be saving as much as me!
E mail me at
to get a rough cost or for £50 I can provide all the instructions for a self fit including materials and where to buy.
I also do bathroom professional 3D CAD designs for a cost of £100 which is fully refundable on purchase with participating stores. Some nationwide so in effect it's free.
I have been a kitchen, bathroom and lounge designer for almost 23 years so your in good hands.
Regards
Colin