I had the same problem as siamesecat .My solution was just to click on every pixel on the build button.
Till it worked.
And the button of the Water Reservoir turned into a gray box when i bushed it to on.
By the way(No Bug but)
If the Space key would pause the game ........Like in FTL ( I love FTL i got 233hours.100%)
,Maybe C for buying coal and Keybinding over all would in my opinion
improve the game.
Yeah i often lost in the second level (ten times ore so)
And i´m not bad at video games
Of course i like a challenge and i liked that Level .But level two woulde be to hard for Normal (or Casual)gamers
So thats hard mode for me : ) .(easy for the creator is often hard for players9
i hope i could help to
give you some constructive criticism.
English is not my first language.....(I´m German)
So forgive me for all my mistakes.(Blame google translate)
In short i like you Game.
and i will help playtest it if you like.( i play it anyway ;) )