To create water shadows in Canva, we first need to analyze the water type, which means shadows would be different for static or moving water. Let me show two examples for which I have created a video recently for your quick understanding.
How to create a shadow effect for static and moving water?
Step 1 - Type a text you want on a separate slide and make a copy of it.
Step 2 - Use font “Glitch” for a second copy.
Step 3 - Download this slide as PNG transparent file and upload it again.
Step 4 - Now add this text on the upper side of the water, crop it half with the main text, If your water is static then flip the main text vertically and reduce the transparency up to 60 or 70% but if your water is moving then use the glitch text with vertically flipped position, also reduce its transparency.
You can increase the brightness of text or make it blurry through adjustment for a more real-looking effect.