When we lived in Davao our water was from Dumoy Water Supply System
Supposed to be the cleanest in Philippines (but I didn't drink it)
What I can say is that it's the coldest water I've ever encountered. Personally i never used a hot water shower as I enjoyed the cold water experience, but all our visitors wanted hot showers

We have a shower heater here in Marikina but I've never used it.

Is there enough water pressure for a shower heater Harry?