Alka Seltzer Plus - Is the white, grainey residue in the bottom of the glass medicine too?

Both answers above are incorrect.
According to Alka Seltzer's Website,
the white grainy residue are inactive ingredients and all the medication is dissolved in the liquid
Same information is printed on instructions and drug info sheet enclosed in every box
It is totally not necessary to consume the residue

Yes it is. I believe there is a warning on the box that let's you know. I just add more then normal amount of water and keep swirling it around until most of it is gone.

Yes it is, swirl it around with a little more water so that you can swallow it all.