Stand sideways to your student audience and then blow strongly through the straw. Water will rise up to the top of the immersed straw where it will be broken up into a spray of droplets by the air stream. You have made an atomizer , somewhat like the rubber bulb operated perfume bottles of years ago. Now invite the students up to each get a cup, etc. You probably will want to have the sponge and paper towels handy.
Small cups limit the amount of water to sponge up when accidents occur.
Almost certainly a student will respond that the water rises up in the straw. For those who are not sure, repeat the experiment with your atomizer, and point out to them how the water in your straw rises up as you blow across its top. Now you should ask them why this happens. Point out that it applies to fluids such as air and water, and then connect any of their statements that may be pertinent to the simply stated Bernoulli Effect. Use a large arrow or two pushing down on the surface of the water in the cup, and a smaller arrow pushing down at the top of the straw.