What's the logic of having to pay for the option of sewage system several times?

[MarkCSA]

As the title suggests: I select the Sewage System option, pay 200€, build two sewers, then my decision mode option disappears and now I have to pay for it again? What gives?

[Ebbingford]

Wait for the sewers to be finished, the option to play those decisions will then be available again.
If you pay for the decisions again via the F4 screen I think you end up with being able to play 4 at a time instead of what sounds like your current 2.

[von Sachsen]

Edit: Already answered.

[MarkCSA]

Hmmmm, activated it again and indeed got to do it 4 times, I think the first time it timed out (if that's possible) after two goes.

Thanks for the answer about it not being unlimited amounts of sewers I could plonk down.