Ok guys, really thanks for all the input, just wanted to update for everybody's future reference because this was scary AF. So this is what actually happened.

Got the Joven technician to come over and check, turns out it is the heater element that was spoilt. But usually if this happens, turning on the water heater would have tripped the current box. However it did not, instead the current was running through the copper piping then into the steel shower head. F*ck.

So, got heater element fixed and then got my electrician to come take a look to find out why it didn't trip as it should have. Turns out the ground wire for the water heater was not connected to anything!  This one is probably due to my previous crappy contractor who did my reno who also installed the water heaters. Was a vomit blood experience but that's another story.

What the electrician did then was to connect the ground wire from my nearby air ventilator to the water heater's ground wire so in future should trip if anything goes wrong. He says should be safe enough. But can also do further precaution by installing RCBO for the water heater at the current box.

Sorry if I have wrongly described anything as my electrical knowledge is nil. Anyways I'm considering getting these RCBO models, all got various prices... any advice?

looking at how TS's electrician installed the water heater and the errors with the DB box.... I'm wondering how many other houses out there are done the same way by the same guy with the same mistake as well? basically all ticking time bomb.....

Hey gobiomani, I've got another question, if my RCCB is 63A 300mA, is it neccesary to get the same 63A? As in a 63A 30mA RCCB?

Yes, thank you sifu! Re: 63A, just wanted to make sure since when I went to the shop, sale staff asked me and I also didn't know how to answer.

Which actually leads me to my next problem... when I was going to all the shops to source for the RCCBs and RCBOs nearly every shop staff gave me a funny look when I asked for 30mA tolerance RCCBs. They said it's too sensitive and will trip often and they recommended 100mA instead. (I know, I know, it's the law and 30mA is what all you guys have been recommending, and yes, 100mA still will con-con-con-con-confirm die )

So question for all those of you that actually have 30mA installed, does it actually trip easily? My worry is that I'm out of my condo for long periods of time often, if trip then things like the fridge might be a problem (with all the food rotting and all).

Well, same issue I faced..

They insisted water heater uses 30mA and when I said ST rule since 1994 is also there already he looked at me and insisted "no such thing ever!"

If you still worry of easily trip (despite the good brands like ABB, Hager won't unless it is a life-threatening leak) then you can continue with 100mA for your lighting and fan, since human are usually not exposed to it. Keep the 30mA maximum for your plug points, and 10mA for water heater.

Bear in mind, you should in fact ensure your steel roof/steel-type awnings are grounded as well (a green wire to connect to your DB busbar directly) for safety - otherwise ((when there is a leak) anyone who climbs the roof to fix/repair something might get electrocuted to death since your lighting/fan RCCB sensitivity is only at 100mA. This also ST requirement actually.
It would be a miracle if people who install awning at his house would get an electrician to help pull a green wire connect to your earth busbar, whilst the awning are fitted with wired lamps/fans.