Water Lily

I know 100% nothing about water lilies. So I have lot of really silly questions which I could probably look up myself. But where’s the fun in that ?   
How deep does the water need to be?
Can you get dwarf varieties?
Does the water need to be flowing at a reasonable rate?
Do the spread quickly/ are they thugs? 

I’m thinking a couple in the ditch at front of our plot. But it’s not very deep. Depending on the weather it’s a very general trickle to not quite a raging torrent. I’d like them to not take over and have their offspring disappear off down stream. 
Is this a possibility or Should I forget the idea?

I know you say your water isn't deep enough even for the small ones, but I thought I'd answer your questions still.
How deep does the water need to be? Anything from a foot down to two meters
Can you get dwarf varieties? Yes, and they're not as thuggish as the others. Try www.lincspplants.co.uk.
Does the water need to be flowing at a reasonable rate? No, they like it in ponds with still water, more than a flow.
Do the spread quickly/ are they thugs? Some are worse than others, but north-ways the cold in the winter knocks them back a bit, so shouldn't be too bad where you are