Silastic 732 or 748 is the pick - food grade and good to 230°C.
The Selleys Enginnering 401 is similar, but takes a week to cure properly,while the Silastic products take 2-3 days.
The main thing with the food gradedness is the curing:make absolutely sure that it has completely cured. This is particularly important with thicker beads. Advice from Dow Corning said all of their silicones are safe for use in food applications, but only the 747 has been certified as such (ie they have paid money for the certification).
If a silicone is suitable for water and the temperature range, the only outstanding thing really is making sure the chemicals that come off during curing are compatible with your material (e.g. Copper maybe not the best with acid cure) and making absolutely sure it has fully cured before putting food/water near it. Ventilation and time is the key here.