Take a swim, feed those hungry steam turbines, dig a moat, or dig canals to connect bodies of water (useful for boat and ship mods).

Additions:

Waterfill - replace dirt with water
Swimming - Players, vehicles, and biters can cross shallow water

Balance:

Waterfill can only be placed adjacent to existing bodies of water - no spawning water from nowhere
Waterfill only produces shallow water, which biters can cross
Water will slow down biters (and players)
Minimum 3-tile width, since this can be used as a high-throughput water pipe for reactors

Disclaimer

I did not create this mod, i just updated it to 0.17 for my personal use and wanted to make this available to others. The original creator is MostlyNumbers, the original mod here.