While filling a container with water, your character is reminded of an incident from the past which intensifies the emotion he or she is already feeling when they start to get water. What the container is, the reason for getting water, and the method of getting water are all up to you – they may (should?) even say something about the character and/or the setting.
Maybe she’s drawing water from the family farm well pump to scrub the farm house windows for the last time before the land gets sold and she remembers her grandfather showing her how to use this pump when she was a little girl.
Perhaps he’s fed up there’s no money for anything but the barest of essentials as he fills a pot of water at the sink to make yet another box of macaroni & cheese for dinner and he remembers the mac & cheese his mom made and he wonders if he’s been poorer longer than he ever knew.
Or possibly she steps out of the hospital room for just a tiny moment to fetch a glass of water for her mother, and catches herself laughing – the first laughter she’s experienced in a week – at how her mother used to leave water glasses all around the house.
If any of those examples are something you’d like to expand on, by all means. Also, it’s completely okay to make this a snapshot, where it’s a scene without a “traditional” beginning or ending. In a way, all of the above scenarios are perfectly valid middles. Give yourself fifteen minutes for this exercise.
Write it up and see what happens.