That's true, but the people could also be doing some other job with their effort too. If you factor in the water consumption of the energy used to power their laptops while answering these questions (~30W of power for 11 minutes per interaction, 1mL of water per W of power) you get another 5mL of water per interaction purely in electricity use.

Not saying it's a 1:1 comparison but it puts it in perspective.