Whisk water, ketchup, soy sauce, tomato paste and cornstarch in a medium bowl.
Heat oil in a large skillet over medium-high heat. Add shallot and cook, stirring occasionally, until softened, about 1 minute. Add garlic, chile and ginger and cook, stirring, until fragrant, about 30 seconds. Add spinach and stir until just wilted, 1 to 2 minutes. Stir in the sauce and crab; reduce heat to medium-low, cover and cook, stirring occasionally, until heated through, about 2 minutes.