How to increase water pressure from rooftop tanks to shower and hot water tanks.?

I live in a 3 story town home, and the only way to get water from the city mains is to have an underground tank because the city has virtually NO water pressure. We use a well pump to pump water from our underground tank to the other tanks on the roof. However, the pressure in the taps seems pretty low. The 2 hot water tanks are on the same level as the bathrooms (second and third floors). The pressure from the hot water tanks to the showers are horrible. Is there a way I could install some sort of pressure boosters/pumps to increase the water pressure from the tanks on the roofs to all the taps/hotwater tanks in the house? Any suggestions are welcome. Oh! And I live in Africa.