This picture shows very clearly the difference between "Eastern" Water Rail - like this one - which has a dark brown eye-stripe and Western Water Rail - the one at Mai Po last month- which had an all-blue face.
Western also has no barring on the undertail coverts, but this group of pictures does not show that so well, while this bird shows barring - on pic no. 4.
Compare with the pic
here to see the difference.
Cheers
Mike K