typical amounts of water?

[Steve Last]

Does anyome know where we can find an indication of what actual amounts of water are needed for typical plants in our region (Vaucluse/Provence). We have been having a problem this year with a significant number of plants dying. Sometimes we will have 4 do fine but then two suddently die from a bos of six apparently identical ones. We suspect that we have either not given them enough or alternatively too much! Also want to set up an automatic system and need to figure out how much to give them on that - watering systems give you litres per hour and so on but we don't know how to set it up so that plants with different needs actually get the right amount to start with.

Steve L