Aside from opening and restoring facilities all over the region, you can also assign factions to look over the facility you just reopened. There are various buffs and advantages depending on the faction you choose so be sure to choose carefully before assigning a facility.
There are 2 main factions in Dying Light 2, which are the Peacekeepers and the Survivors. Each faction can give a different buff or advantage depending on who you choose when assigning the facility.
Facilities can be unlocked by doing main storylines or creating safe zones across the map.
Unlocking and reopening facilities like the Water Tower can help create safe zones. You can find the facilities you can clear out and reclaim on the map.
However, assigning them to either faction means that the faction will own and run that facility. Early on in the game, you do not need to worry about this. However, once you reclaim the Water Tower, you will need to decide.
When you reclaim the facility, you can assign it to a faction.
Generally, Peacekeepers will install car traps and Survivors will place air vents on the zones they control so choose whichever you prefer.