Hello,
The water temp at the moment is 16'C (
http://www.maltairport.com/weather/ for weather report),in March it will be 14'C.A 7mm semi dry should be perfect, but as always depends on your body as no one fells cold same way. Me normally use a 5mm wetsuit longjohn and jacket for dives up to an hour, and also use a drysuit with a 100G undersuit.
If you need anymore info just mail me