Your first point.  Eliot has skilfully used the tarot cards for
a) laying out the major symbols/themes that become subsequently
   operational in the poem;
b) to repudiate the secular aspect of contemporary civilization
    (represented here in the character of Madame Sosostris) which
    is blind to the spiritual aspect of these symbols.
You're right, Eliot places great value upon "death by water".
Madame Sosostris has the power to predict it but she cannot
decipher its spiritual value -- hence her note of caution.
Your second point. The dual aspect of "water" in Eliot's
poetry has always fascinated me -- as water of passion(s),
or as a purifying/redeeming/transforming agent.
In Part I, Isolde is lingering over the seas of passion
and the sailor's song sounds a note of caution.
In Part V, the seas of passion are "calm", if one's hand is
"expert with sail and oar", i.e. if one has control over one's
As a purifying agent, it is part of the washing ceremony at
Chapel Perilous.  As a transmuter, "Those are pearls that were
his eyes. Look!" And as a redeemer in Part IV.
In TWL, the yearning for water is both literal and figurative --
(a) the need to quench one's physical thirst, as well as to dispel the
dryness of the land,  and (b)  the need for emotional and spiritual
It would be interesting to watch this duality in Eliot's use of
the "wind" too -- but for that one will have to look up some other
poems too in addition to TWL. 
I must thank you, Diana, for raising this issue.

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