Coolant Light - Renault Clio (W reg)?

Hi.

Sorry to be completely useless, but the coolant warning light has come on twice in 2 days in my Clio. Handbook says to fill it up, but does not enlighten me as to what with.

Is this just with tap water, distilled water, antifreeze???

Have recently found drips on our driveway that I thought was an oil leak, but could it be that the coolant is leaking?

Thanks in advance.