[philonossis]

I bought a small hand-held water heating coil,

the type designed to heat water in a cup to make coffee tea, etc.

It is supposedly from China.

After a few uses, a white powdery residue built up on the coils themselves. One the coil and a little above the water line but not all the way up to the handle, i.e, not completely covering the metal part.  Therefore I think contact with the water has something to do with the formation.

The coils in their clean state look to be stainless steel.

There is a plastic handle and the unit plugs into the wall socket.

This white residue will come off on my fingers

I am using Nestle brand drinking water to make coffee, not tap water. The cup is completely washed before each use, so there is no residue from coffee, creamer, sugar etc.

Does anyone know what chemical this residue would be, and if it is harmful?

[Borek]

This is limescale. Don't worry.

[Ari Ben Canaan]

This is limescale. Don't worry.

I would guess that it is limescale caused by dissolved magnesium and calcium ions.

The build up of this limescale MAY damage the heating element and hence device.

To prevent it I've been told adding citric acid crystals is the best method.

[Borek]

The build up of this limescale MAY damage the heating element and hence device.

Highly unlikely in the case of this type of heater.

To prevent it I've been told adding citric acid crystals is the best method.

Add them to what? Boiled water? How are you going to use water with added citric acid to prepare a coffee?

[Ari Ben Canaan]

The build up of this limescale MAY damage the heating element and hence device.

Highly unlikely in the case of this type of heater.

To prevent it I've been told adding citric acid crystals is the best method.

Add them to what? Boiled water? How are you going to use water with added citric acid to prepare a coffee?

I've learnt that accumulation of limescale on the heating element may cause the element to overheat.

You make a good point.... citric acid and coffee dont go well together.

[philonossis]

You make a good point.... citric acid and coffee dont go well together.

Actually lemon juice tastes ok in coffee.You can add it to espresso with sugar but no cream. The Italians call this a "romano."

[philonossis]

This is limescale. Don't worry.

thanks to Borek and Ari for clarifying this for me.

[philonossis]

This is limescale. Don't worry.

Something new has appeared.

Now shiny metallic flakes are being deposited in the bottom of the cup after I bring it to a boil.

I may be wrong but this does not seem be just lime. It looks like it may be the surface of the heating coil itself exfoliating, but I cannot be sure.

Since magnesium is a metal, could these shiny metallic flakes be magnesium?

Regardless of what chemical they are, would these metallic flakes be harmful to ingest?

[Borek]

I may be wrong but this does not seem be just lime. It looks like it may be the surface of the heating coil itself exfoliating, but I cannot be sure.

Not magnesium, throw the heater away. Not that these flakes are very toxic, but digesting them is not a best idea, besides, the heater will now corrode much faster.