Land in water dissolved evenly (4)
I believe the answer is:
isle
'land in water' is the definition.
(an isle is a bit of land surrounded by water)
'dissolved evenly' is the wordplay.
'evenly' indicates alternate letters (the letters in even-numbered positions).
The alternate letters of 'dissolved' are 'ISLE'.
(Other definitions for isle that I've seen before include "eg Thanet" , "Spot (in ocean)" , "Lilliput, say" , "See 11 Across" , "Perspire" .)