In the original mod, the highest tier was able to absorb 2k pollution per second, which is a lot more than what I can achieve here. Now while I am sure a lot of people are fine with filtering this amount of pollution, an omega drill (mod) with 3 productivity modules and only some speed module beacons around it spits out 3.2 k pollution per second.

Are there higher tiers planned (the idea with water instead of filters sounds cool)?

I'm not planning on adding features to the mod anytime soon. However, anyone is welcome to implement changes or new features and to make pull requests to the source code.
The mod may need some balancing changes, especially towards the late game when considering modules and interactions with other mods.