Stealing heavily from the Waterfill and old Canal mod, I've made Waterfill a little less OP. It's not (as) feasible to build a massive moat around your base anymore thanks to some of the changes I've made. First off, the recipe is much more expensive, requiring concrete, explosives, and pipes in addition to water. The technology research is also more expensive, requiring blue science packs and more of them after unlocking concrete and explosives. The crucial change is that any attempts to use waterfill without it being placed adjacent to existing water tiles will cause your waterfill to "evaporate", costing you the items without placing your water. Waterfill also cannot be placed by robots or included in blueprints, and the stack size is limited. It is exclusively intended to allow for neater, more aesthetic water pump placement for builds that require water, not to isolate your base or biters from each other as an OP defensive measure. You will still be able to practically severe an isthmus, but anything larger should be fairly impractical.

It's my first modding attempt, so I apologize if I stepped on any toes or if there are any bugs, like me breaking landfill in the prior version.