Just about anything that can hold water can be used for the splash pool but different shapes have different properties. For eye level shots; CD container lids, salad bowels, large glasses, cups, soy sauce saucers, all work. For angled shots with a reflection; baking trays, seedling trays, purpose built large flat acrylic trays work well.
The different sizes have very different properties. The smaller bowls are good for simple Worthington Jets using smaller drops and the larger bowls are good for taller jets using larger drops.
This one was taken using the 14cm bowl. The the second largest bowl in the photo above. This bowl is 6cm deep and good for jets produced from large drops. It is not so good when using small drops.
For small drops I get much better results with the smaller bowls or the trays.
This is a 2 drop collision using larger drop sizes. The first drop size was around 60ms, the second drop was around 55ms.
If you want to know why 60ms is good see the First Drops guide. The picture has been cleaned up slightly (I cloned out some stray drops).
The soy sauce saucer gives very similar results to the small glass bowl but holds far less liquid. This is about the tallest jet I can get from it through.
Note: The camera position and angle plays a large part.
I had a couple of trays made from 4mm clear acrylic. One is 80x40cm and the other is 60x30cm. I also bought black and white acrylic sheets to use as inserts. I use these trays as the splash pools and also as spill trays when using smaller bowls.