Second Normalized Difference Water Index (NDWI2):

NDWI2_2017
($3.B3 - $3.B8) / ($3.B3 + $3.B8)
NDWI2_2018
($4.B3 - $4.B8) / ($4.B3 + $4.B8)


Sentinel Water Mask (SWM):

SWM_2017
($3.B2 + $3.B3) / ($3.B8 + $3.B11)
SWM_2018
($4.B2 + $4.B3) / ($4.B8 + $4.B11)


Water Mask:

WaterMask_2017
if (($3.NDWI2_2017 > 0.3) or ($3.SWM_2017 > 1.0)) then 1 else 0
WaterMask_2018
if (($4.NDWI2_2018 > 0.3) or ($4.SWM_2018 > 1.0)) then 1 else 0

Water Change:

WaterChange_2017-2018
$3.WaterMask_2017 - $4.WaterMask_2018