Use a compatible replacement rather than an unverified adhesive repair to a drinking-water reservoir. The material, food-contact suitability and sealing strength all matter.
What the observation tells you
A crack may extend beyond the visible line and change when the tank is loaded or moved. Adhesive can also prevent the outlet or lid seating correctly. A temporary appearance of being watertight is not confirmation of safe long-term use.
A useful next step
Stop using the damaged reservoir, empty it safely and identify the exact appliance and tank. Keep any leaked water away from electrical fittings and obtain the correct replacement specification.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.