[positiveion]

A tanker of acid is emptied into a water supply by mistake. A water company chemist titrates the water and finds that 10 dm^3 water are needed to neutralise 10.0 cm^3 of .010M NaOH. Calculate the concentration of hydrogen ions (H+) in the water.

I don't even know where to start.

[Borek]

As usual - start with the reaction equation.

http://www.titrations.info/

Just note - you don't need to know what acid it was, as H⁺ is all that will react (go net ionic).