The Dam
The reservoir is held not by discretion but by written rules — constitutional plumbing deciding how much may flow out and who can open the gates. Four load-bearing pieces:
Net Investment Returns (NIR) framework
The Constitution allows the Government to spend up to 50% of the expected long-term real rate of return (ELTRROR) on relevant assets — the net assets invested by GIC, MAS and Temasek, minus Government liabilities.
Expected, not realised
NIRC is set from expected long-term real returns projected by the investment entities and concurred with by the President — not from any year's actual result. A bad year does not cut the Budget; a good year does not raise it.
The second key
The President's concurrence is required before the Government can draw on Past Reserves — reserves accumulated during previous terms of Government. The President has veto powers, access to full financial data, and oversight of key appointments.
The secrecy is a policy, not an accident
MOF's stated reason for not publishing GIC's size: taken together with the published assets of MAS and Temasek, it would amount to publishing the full size of Singapore's reserves — information the Government holds back for reasons it argues are strategic.
The tension the rules encode
A spending rule based on expected returns smooths the Budget, but it moves the argument onto the one number the public never sees debated: the expectation itself. Raise the assumed long-term real return by a single point and billions in additional annual spending become constitutional. Those projections are made by the investment entities and concurred with by the President, and their value is not published. The dam is real and it holds — but its most important gauge faces inward.