The Young's double slit experiment belongs to a general class of "double path "experiments, in which a wave is split into two separate waves that later combine into a single wave.In water λ is reduced to λμ so λ' so λ' =λ16As ω=Dλd∝λ      ω'ω=λ'λ=λ16λ  or ω'=0.81.6=0.5mm