Raising the map's water level would reshape the whole settlement. The plan involves building around the map and probably filling low ground to bring more land up to the new level. That would mean producing soil and reaching the stage when golems are available. Extra water storage therefore depends on construction and technology elsewhere in the settlement. The larger reservoir is a possible later development whose supporting work must be planned in advance.
Notable Point · 11:52-13:41
Why raising the reservoir requires more than another dam
Larger water reserves would require construction around the map and probably soil production to raise the surrounding low ground.