Risk assesment is all about being able to demonstrate that you have considered the possible risk to others that your activities pose. There's no need to get worried about it - I would suggest that you make a list of what risks you might pose ie trip hazard from hoses and maybe a slip hazard from lying water. Then list what you propose to do to minimise these risks - ie cones or maybe taping off the work area. It might be also making some notes about any hazardous solutions you might use - even make a note of the fact that there aren't any!
Good luck!