TL;DR
I want biters to drown themselves in case they can't pathfind through water and eventually create a biter-corpse landfill that they can cross.What ?
Factorio's water gives the player the biggest exploit against the game's only dynamic threat - biters. By carefully planning where to expand in relation to bodies of water, you can easily create chokepoints, murderholes, that are impenetrable and never worry about the biter problem. It's especially abusable if you created a map with large bodies of water. Than you can just create a landfill island, that is practically unreacheable to biters. So, what if biters could pass through water, but not just by swimming but in more "brutal nature" kind of way?In case a biter swarm can't find a way to the source of pollution around the water - they would just run into the water and drown. Water tiles where biters drown would have a counter, when if reaches a specific amount, the water tile becomes walkable (but not buildable), because of all the accumulated biter corpses in the water.
Now that's simple and also requires a perfectly isolated island base, but what about chokepoints? Well, I propose that after a certain amount of biter deaths in an area, biters pathfinding should avoid it. So, if you have a perfectly defended chokepoint, eventually biters stop going there and try to find another way in. So even if your base has land access and is only partially protected by water - biters are still going to eventually try and breach this water barrier, since it's not protected.