It may be said that unconditional love is not an immediately apparent aspect of Aquarius, which is ruled by Uranus and Saturn.
But, apart from the fact that the spiritual knowledge which the water in the jar is said to represent is all about love, there are several astrological aspects which relate to the planet Venus which represents love.
In the myth of Uranus (the sky god) he is married to Gaia (the earth) and is castrated by his son Saturn who conspires with his mother Gaia as revenge for burying her children deep in the underworld.
Gaia is represented by the Zodiac sign of Taurus which is ruled by Venus.
Aphrodite was said to be born, like the foam of the sea, from the severed genitals of Uranus.
Aphrodite (Venus) rules the zodiac sign of Libra.
So both Taurus and Libra - the two signs that are ruled by Venus - feature prominently in the myth of Uranus.
It may be said that Uranus regains his power (his severed genitals) through love (Libra/Venus) and is thus reunited with his wife Gaia (Taurus/Venus).
Traditionally Aquarius is associated with brotherly love or universal love but the unconditional love of Taurus/Libra gives power to Aquarius and harmonizes with the other aspects which relate to love in the symbolism of Aquarius.