Making water safe to drink & transporting it to your door uses much energy & chemicals, too. Even if you live in a place with lots of water, it creates pollution indirectly every time you use tap water. So everyone should conserve, where possible, ideally, to minimise pollution & use resources wisely.
Can I use washing up water (no dishwasher) to water the plants?
Yes, though probably better if you use washing up liquid with minimal perfumes in it.
What about water that is left in the steamer or saucepans from cooking veg? Can that be used for the garden too? Yes, also can mix with fruit juice for toddlers to drink, or cook rice or make pastry with (not minging if next day). Full of vitamins that shouldn't be thrown away, too.
What water shouldn't we be using on our garden? Not Washing machine (clothes). Dishwasher would be ok, I think, but hard to recycle & minging to store.
it amazed me how much water I was wasting just from running the hot water tap. We use that cold water to flush toilets, often.
I too am interested in grey water - bathroom window is above my side alley so do I just suck on a hosepipe and pour it into a bucket below?
Yeah, but it's minging & hazardous to keep for long. You can bucket water out of the bath to flush toilets, or put a bucket in the shower to collect run off & flush using that. Warning: the hot water leaves more limescale than cold water.
For garden, Waterbutts to collect water out of the guttering are good, they get minging occasionally, we end up cleaning our butts every 2-3 yrs, but still much nicer than household waste water.