This was so fun to watch!
It was especially helpful to see what you and your friend found confusing. The filling/depleting of the water resource has tripped up many players, so I can tell it should be made clearer. You did eventually realize that you need to splash hydrants with balloons, but there's not a clear animation or sound effect when picking them up, so it's hard to tell.
There was another mechanic that snuck by unnoticed, which is that driving on sidewalks causes water to leak. Although there's a sound cue when hopping a curb, the visual feedback for this mechanic is vague, and there's only a brief mention of it in "How To Play". Still, I felt this mechanic was important to include, because it gives the Tiller more purpose by giving them some responsibility for maintaining the water supply.
Again, thanks so much for sharing your playthrough video!