Can my SPX2690-SJG unit be connected to a portable water supply?

Your pressure washer must be connected to a main water supply with a main pressure system providing a constant inlet pressure up to but not exceeding 0.7MPa (7 bars, also equal to 100 psi). Portable water supplies, tanks, and pumps use regulators that cannot provide a constant pressure to your unit, and this will cause the motor to wear prematurely, or even break entirely.