Electricity, water
After slightly more than dozen of minutes which means few weeks in the game coal plant that you placed at the beginning will start having some efficiency problems - despite increased spending on electricity, it won't generate more of it.
By then, city should reach the point in which advanced wind turbines are available. Though they have prices similar to coal plants and they create half their amount of electricity, they have three important advantages - they don't generate pollution, they are placed on water which means they don't block precious land, and, most important, they are cheaper in maintenance than other plants.
Other possibilities you should explore are hydro power plants and solar power.
Only thing related to water that should be done except for gradual growth is replacing drain pipes with water pumping stations when they become available.
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