Hello,
Yes, normal is much too hard I feel. I play on easy 80% building cost. But I tried this strategy on normal, and works there as well. But it's very tight, and almost no wiggle room. Quite stressful, I feel. :-(
- without any "extension" is possible to reach 50% coverage! Just use the mountain carefully as well.
- start from mountain top with a water pump. This fills more water that way.
- always postpone building greenhouse, until all toxic scrubbers are placed around that particular area
- I was building from mountain top to bottom. And placing carefully on mountain as well. The toxic scrubber and greenhouse also ignores the terrain - except the hill walls themselves. So you can plan them smarter this way. (Also, in 2th stage, all mountain coverage is very important.)
- On the plains section: don't worry, if you don't cover everything to the edge of the map. Just keep in mind the large scale, and maximalize the coverage around the rivers. It will suffice in the end. Trust me.
- Don't worry too much about greenhouse not having maximal profit. They are cheap, and the main goal is the maximal coverage. It's cheaper to have multiple greenhouses to cover all clean area, than cleaning more area - which means bigger power coverage as well! (This is also true about the Toxic Scubber. However, they are more expensive. But a little cutting back on the covered area is less "expensive", than "making more land" with power coverage.)
Screenshot from normal: