I have seen in Condo, they installed rain shower without pump. The key points are your incoming water pressure ( around 3 bar, i think )

and also the water flow rate, at least 13 liters/min for rain shower.. Check with your management office..

Depending on the condo some is like 4bar from syabas incoming to underground feed tank. Then from this common UG tank it is pumpednto roof tank. Roof down to unit usually pressurised enough for rain shower, but one can experiment in 1 min how many liters of water can you fill up.

For mine (even if its just a rumaweep) the pressure is good enough (even setting 50% at the main valve for my unit) to max out the heater power at 90 100%