I recently replaced all the belts of my Honda Civic (mileage 94,000km), including the water pump belt.
Soon after, I discovered a water leak in the cooling system. The workshop traced the leak to the water pump, which was replaced.
I have two questions.
First, is the water leak related to the belt replacement?
Second, the cooling system, which was completely drained, now has clear water instead of the previous green liquid. Is this okay?
Yes, the water leak is related to the belt replacement. When a new belt is installed, the mechanic will inevitably tension it by imposing some degree of load - a new belt has stronger tension - on the water-pump drive pulley.
If the pump is an old one, this will cause rapid additional wear in the shaft seal, leading to water leaks.
At the mileage you have stated, it is a good idea to replace the water pump at the same time you replace all your belts. The mechanic who installed the new belts should have recommended this.
As for your second question, filling the car's cooling system with plain water is definitely not the right thing to do.
You must have the appropriate volume of coolant, not just as an additive to raise the boiling point but also as an anti-corrosion agent.
The coolant also has lubricating properties. This helps to reduce wear on the water pump shaft.