@temporal_spider i was gifted one of the Sakura field kit sets and it's perfect for limiting the mess. The included water brush solves the water issue - that does limit the technique a bit since it has a certain flow rate, but if you really wanted to add more water you could also use an eyedropper. You can also mix the pan color with watercolor pencils - those will activate just by touching the tip of the pencil to a wet brush, producing bold lines of color.
https://www.sakuraofamerica.com/product/koi-water-color-field-sketch-kit/