Increasing your Housing can be achieved by the following: Buildings, Civics, Districts, Tile Improvements, access to water: being next to Rivers, Lakes, Oasis and some Natural Wonders, by building an Aqueduct (which must be placed adjacent to both your city and one of the preceding freshwater sources or a mountain), and or lastly Great People. The Tile on which the city was settled also influences the starting housing limit number, so if a city has access to fresh water it starts with +3 Housing. If it has access to the Coast it has +1 housing, and if it has no access to water it gets +0 to housing.
Whenever a Settler is selected, the non water tiles in the map will be marked as one of the 4 colors: Red (the Tile is not possible to settle), Grey (The Tile has no access to fresh water), Light Green (The Tile has access to the Coast) and Dark Green (The Tile has access to fresh water).
This is a new aspect to consider when settling new cities: the Water Availability Guide. The Aqueduct District can take fresh water 1 tile away from Rivers and Mountains providing fresh water to cities. Cities which have access to fresh water gain +2 housing from Aqueducts, while cities without access will get +6 housing.