It's just a little puddle to wet your socks. To be honest it's annoying when you are running.

I can't really change that, since the puddle just uses the water fluid.

I forgot to mention that I got this suggestion after playing with Unearthed mod - it adds puddles (only generated by entering/leaving the water, not by rain) which don't slow don't your movement. They also have Targeted Fluid - minecraft:empty and for yours, it's water like you said. Maybe you could take a look at their implementation?

Is your mod server-side only? I'm not sure because it uses vanilla water but at the same time there is an obtainable (via /give) block so probably no.
Can you add information about the available config option (/gamerule) to the curseforge desc?