Installing water-efficient devices in apartment buildings is not always as straight forward as doing it in a house. The following paragraphs summarise some factors that may need to be taken into consideration for your building.
Don’t let them put you off. It’s just a matter of having the discussion with your service provider up-front to determine the best approach for your particular building. That way you’ll reap the rewards, and avoid any problems for your residents.
High-rise buildings have distinct water pressure gradients as you rise through the building. After roughly the first four floors, mains pressure water will typically be no longer suitable. Floors above this point will need to be supplied either by a pumped supply from a ground, or basement level storage tank (which is in turn, filled by the mains) or, more commonly by a tank on (or in) the roof of the building that then supplies most remaining floors via gravity. The four or so floors directly underneath the tank in the rooftop water storage scenario, then also need to be supplied with water from a pressure-boosted system via a pump.
These different supply 'zones' within a building can sometimes present some challenges for water-efficient devices when they are only installed in some of the water fixtures in the building. The issues amplify if hot water is supplied via a different system. Sometimes hot water is circulated centrally and sometimes there are individual hot water units within each apartment. There may also be other configurations. Water-efficient showers especially will struggle when there is a significant difference between the hot and cold water pressures. This is the basis for their incompatibility with gravity-fed hot water systems.
The solution would typically be to not install flow regulating showers in certain floors of a building where the pressure differential is greater than the manufacturer's recommendations. Other water-efficient fittings are generally not as problematic, given the potential savings versus the relative ease of adjusting the taps and the lower risk of discomfort if the temperature balance isn't maintained.
There may be limits to what can be done, but a start would be to try and track down the hydraulic diagrams of the property - these would show how the water supply within the building has been designed.
Typically, in the worst circumstances, only parts (ie. specific floors) of the building would present problems that would be expensive or difficult to overcome.