A lot of water can go down the drain waiting for hot water to reach apartments from central hot water systems.
A very large amount of energy (gas or electricity) goes into heating hot water. Anything that reduces hot water use (such as lower flow showers, taps or washing machines) will also save significant amounts of energy. The energy cost for hot water is often 2 to 4 times the value of the water.
Centrally heated hot water is normally pumped continually around a ‘recirculating loop’ so that hot water is never too far away when it is needed. The loop (always full of hot water) extends throughout the building, with individual feeds radiating to each apartment. High losses can result from uninsulated or inadequately insulated hot water system pipes - from the storage tank and long pipe runs making up the loop and apartment feeds.
If you have cooling towers installed close to your hot water boilers, you might consider installing a heat exchanger to use the heat from the condensers (going into the cooling towers) to pre-heat the water going into the hot water heaters. This has the added benefit of reducing the load on the both the boilers and cooling tower.
A co-generation system, which produces power and usable heat to heat hot water, is the most efficient central hot water system to install.