This is our latest set up. Always a towel under the water tub and tray. The tub is filled with water (about half) and the tray (which really is anything big enough to hold the containers and utensils) sits next to it.
The waterproof apron comes from Montessori Services and is very helpful for keeping clothes dry.
An ice cube tray holds pieces of a sponge. The pieces float around the water tub or can be squeezed with hands or a garlic press.
A variety of containers all different sizes allow experimentation with volume and size. One container has a cap for shaking and "making bubbles."
Funnels are used with the containers. I've seen my daughters put the sponges in the funnels to absorb the water poured in and sometimes they just use the funnels.
My daughters ask for soap sometimes to play with bubbles. More bubbles can be made with the whisk or by sponge squeezing.
Transferring water utensils.
Everything is stored in this box. I try to let things air dry before putting on the lid but the drilled holes in the lid allow for the materials to continue drying.
Water is a great sensory experience. It also tends to calm and relax- I love to watch the concentration as they pour and play in the water. A younger child may be overwhelmed at first with all of these options and could benefit from introducing one or two at a time.