I always reuse water for houseplants, ie half drunk glasses of water etc.  But things like water which has had detergent in it (albeit Eco friendly detergent) does anyone reuse that for plants? Is it suitable? 

What other ways are there to reuse grey water?

I heard on the radio or somewhere that it is fine to use old washing up water on plants IF it is on open ground (ie not pots/tubs where the sediments etc will build up) and I guess if it is not too greasy or bits in it (may attract vermin). Grey water can be stored and reused but that needs more of a plumbing job!

I put the excess water from my tumble drier on my money tree and have right royally killed it :(.  I think it was the residue of washing powder which isn’t an eco brand.

Also will depend what you are watering and the plants own requirements. Some plants will only thrive on rain water - either due to chemicals or usually water pH.

You can use grey water on your garden, some plants may be sensative, but normal veggies and fruit trees/bushes, the lawn etc should all be fine, especially if you are using rapidly bio-degradble eco detergents and using the minium amount.  You are not ment to store it though (like you can with rain water) as it goes manky (that is not the technical term).  I am lead to belive that in countires where water is more scarce (like Spain) sinks have always in the past just had a bowl under the plug and the water was used in the garden.

If you intend to use untreated greywater in your garden then it is essential to reduce the amount of fertilizer you use. Soaps and washing powders contain nutrients such as nitrogen and phosphorous, which should be removed if you intend to use large quantities of grey water in the garden.

Grey water watering systems should be installed under the ground (sub surface irrigation - the most efficient way to water plants) since greywater can contain disease-causing pathogens which you don’t want to spray around your garden.

You should avoid using grey water on your vegetable patch if you intend to eat any of your crop raw or lightly cooked (including herbs and fruits) unless you first filter the water well using a DIY sand filter or commercial alternative.

Greywater tends to be alkaline, whereas collected rain water is acid. Therefore it is necessary to understand which plants thrive in which conditions and to organise your garden and watering accordingly.

According to: http://www.reuk.co.uk/Greywater.htm