If you have an exhaust leak, you aren't going to need water to find it. You will hear it. If it's anywhere upstream or near either of your sensors, you would have a check engine light for it. Generally speaking if it's up towards the motor it will be a sharp cracking or clicking noise. A lot of people mistake it for valves. It would most certainly activate a downstream sensor. If it's in the back it would just be noisy. It wouldn't particularly have a tendency to make the car run badly downstream, just sound loud.
Where I don't know this car specifically, what I would check would be plugs/cap (or) coils/wires, PCV valve, and your catalytic converter for collapse. Normally on the last you will hear a weird metallic vibration sound. Typically when a CC goes out it will smell weird and you will note bigger issues under load or power as it restricts exhaust flow.
Keep in mind that modern cars know issues exist typically even before it becomes a detrimental issue. If you have a CEL you should pursue that first.