The high rise Bangkok condos that I have lived in (including the present one) all have a reasonably large reservoir on the ground level hidden away from sight. The water supply from the mains fills this reservoir all the time. A high level sensor has been fitted in the tank, so the handyman can close the main filling valve if it gets full (I have never seen that happening) Powerful pumps then take suction from this reservoir and pump it all the way up to water tanks at the top of the building (present condo I live in is 40 floors high, with the supply tanks on the roof).
Water pipes then lead from the roof tanks to individual units. The lower the floor, the better the pressure due to greater vertical distance which the water falls to. For the 36th-40th Floor, as the water pressure will not be so great due to shorter vertical distance, a special booster pump has been installed to boost the pressure in their lines.