Water when its drying out - no rules as it depends on the weather. If its moist don't bother, if its dry water it. The bigger the veg the more water it will need but you can always tell from the state of the soil. If you really can't trust your own judgement you can buy a soil testing probe that will register moisture, light level and pH.

One good soaking is much better than a light watering every day as that encourages the roots up to the surface rather than going deeper, but in really drying weather every day might be necessary.

We grow veg in raised beds, and water twice a day in dry spells, but the soil mix we use drains freely, so that may not be necessary (or good) in your case.

Thank you Rosierose, Snoopdog and Steragram for your help. My soil does have a lot of compost in it. It does feel dry though I think my tomatoes have grey mould which means I have been over-watering! On the other hand my courgettes are doing nicely.