To my surprise I couldn't find options to install a storage water heater that can centrally provide heated water to all bathroom

I went to HomePro, Harvey Norman all selling those instant water heater.

I don't want to use those cos need to hack bathroom, pull wiring, ugly and comes with electrical hazard. I want to use back original shower head

Those tank one I see a lot of benefit however I have lots of questions

1. Can my existing PPR pipe allow the installation?
2. Do I install one in each bathroom above the ceiling or can install one at the incoming main?
3. Where to shop for this?

In Singapore this seems to be common. Got option to go with slim design to hide it

Centon brand come with tank for each room or multiple room
check their page

Joven

or

Alpha

52 ltr tank

1. Can my existing PPR pipe allow the installation?
Better check with your property developer / management if your existing pipings can withstand hot water up to 80°C to 90°C for the storage water heater's outlet, else u can get CPVC or copper pipings. Don't cheap out on good pipings, else it will be a big headache if it burst / crack / melt.

2. Do I install one in each bathroom above the ceiling or can install one at the incoming main?
The further away the water output (showerhead / faucet / basin) is from the storage water heater, the longer distance the hot water has to travel, causing a lot of wasted heat loss (in addition to the extra hot water pipings you have to setup). With that reason, better to get 1 storage water heater for 1 bathroom, unless the bathroom is next to each other.

3. Where to shop for this?
U can easily get it from Shopee / Lazada, and u can even read the reviews to help u make an educated decision on which one to purchase. The online sellers should also be able to recommend u installers as well. So far on Shopee it looks like the best seller and highest review is Centon, this one.

Currently I think there are 2 types of storage water heater tank technology,
a. Enamel-coated technology - newer technology, better leak resistance, and cheaper. Brands like Centon and Alpha are using this newer technology. Centon I think launch much earlier in this market and with better experience, better reviews online, and slightly cheaper than Alpha as well. Hence Centon is the better choice.
b. Stainless-steel technology - old technology, more prone to leaking, and more expensive. Brands like Elton and Joven is still using this old technology. Not recommended.

Lastly, be prepared as storage water heater's installation cost is expensive, and might go up to the same price as the storage water heater, if you include plaster ceiling cut and reseal. Again, better don't cheap out and get super low cost unqualified installers, as their might give u lousy wiring cables, pipings, or even worst wrong installation and might cause danger to the people using the shower.