"I need to clean the house on Sunday."
Translation:Jeg må vaske huset på søndag.
Forgive the non-connection here, but it's not just English people who have trouble translating and learning...My Norwegian guests today want to go to London.. to shop at "Horrids"!
Yes, that works as well. It would have a different meaning than "må", but they're both good translations of the English sentence.
Does this mean that I'm tidying up by picking up and putting things away or that I'm using soap and water to scrub the house?
"Vaske" refers to the latter, soap and water. The first (putting things away and tidying up) would be "Jeg må rydde huset på søndag"
I have in the back of my mind "ren og pen" clean and tidy. but å renne isnt a word?
It's a word, but not the one you're looking for. "Å rengjøre" means to clean.
No, we wouldn't say that, but "Kan jeg la vannet renne?" works if you're planning on keeping it running for a while. "Kan jeg la vannet stå på" is another alternative.
You kan also use it to describe the water in a river or a creek, or the waterway itself: "Nilen renner ut i Middelhavet".