Probably a polyacrylamide gel that you get in some composts that retains water
(used in hanging baskets etc)

When I was at college a lecturer was telling us about this gel. As most of you
will know it comes in a crystaline for and is mixed in with the compost when
doing hanging baskets, etc.

Anyway, he told us of when this product first came out. A local council's
parks department decided to get some to add to the compost used for its summer
bedding outside the council offices. The idea was that the gel would retain
moisture during the summer so that the council workers didn't have to keep
watering the beds outside the offices.

However, the workmen didn't bother to read the instructions which accompanied
the gel/crystals, and when the first rain fell the council office staff were
greeted at work in the morning by huge quantities of clear gel oozing from the
raised flower bed. It proceeded to flow over the raised wall and drip down the
steps in front of the offices.

I shall of course refrain from mentioning which council made this blunder, just
in case anyone works/worked for the council in question.

Dave.