25
Get them separate.
Have the goverment tax the living hell out of apartments in scertain areas near colleges, universities, and important work places, like powerplants, labaratoria, and airfields.
Give students and people who work at the jobs you favour as important, as a goverment, tax exemption for their apartement soo they can live them.
Then, use the taxening to hoard all your sub-humans into slums, and you guessed it! Pump their drinking water full of anticonceptives!
What do ya think?