Well, I checked with my friends from PUB reservoir management. Sorry that you had an unpleasant experience at Pandan reservoir. In the past, the reservoirs were restricted and public access is limited, as they were considered key resources ( well, we don;t have any natural resources.Recently, the reservoirs have been open for public use to the extend of using the water bodies for water activities, which in the past was not allowed.We are most welcome to take photographs in the reservoirs. The only restriction is not to photograph PUB installations, which are considered as high security installations in Singapore. That's why we now have security guards at such key installations.
If you need further clarification, you are free to call the PUB-One, PUB customer service hotline or visit the PUB website,
http://www.pub.gov.sg.
Thanks.