Magnesium anode?

[oldworld]

I have a small electric water heater that feeds the kitchen sink and it's now leaking. I've looked and it's leaking from within, the connections are all watertight.
It's a simple installation and I can get another small (15 litre) heater from a large DIY store.
Reading the blurb it mentions changing the magnesium anode every two years. I've never come across this before and wonder where you fit it and where to get one.
Hoping someone has some knowledge they can share.

 

[Nibor]

It will be a sacrificial anode attached to the tank so when a battery effect sets up with the water it will corrode and not the tank. Looks like yours has worn out and the tank has corroded instead.

 

[keithmac]

They have similar on boat engines to stop corrosion.

 

[oldworld]

It will be a sacrificial anode attached to the tank so when a battery effect sets up with the water it will corrode and not the tank. Looks like yours has worn out and the tank has corroded instead.

Have you any idea where to get one or where to attach it?
I had a similar thing on an outboard engine but that just bolted to the casing.

 

[Bazzer]

Ebay seems to have some, for example. But there are other suppliers, which may depend upon both your application and what the existing one is like.