I swear by having a general purpose capillary system involving matting on a raised platform (fake slates on polystyrene are good) inside a tray slightly larger so there's space to put a 'budgie waterer' made of upended bottles full of water (milk bottles aren't stiff enough). You add bottles until you are confident it can be left for a 2 week holiday whenever you take it... Wide necked bottles are an advantage for stability.
Could you explain how to make these "budgie bottles" in very simple language please as my attempts with bottles never seem to work that well.
YouTube has tons of stuff on wicking/capillary for plants and almost as much on budgie bottles - but tailored to actual animals. I couldn't find anything that combined both ideas. Maybe someone else can find one...
Short of going to a pet shop or recording something myself it's simplest to describe an experiment I was shown in my earliest chemistry lessons when I was 11.
Demo:Put 30-50mm of water in a washing up bowl.
Take any fizzy drink bottle (it has to be reasonably stiff - milk bottles are useless) fill it with water and put your thumb over the full bottle so you can turn it upside down, immerse your thumb and the bottle neck in the bowl and release your thumb.
The bottle will stay full of water.
You could demonstrate what would happen when a plant drinks all the water in the bowl by ladling the water out - but it's easier to hold the bottle in one end and tilt the bowl so the water goes to the other. The bottle will stay full until there is no water under the neck. When the water in the bowl is below the neck the bottle will start to empty. As soon as you let the water back it will stop emptying. In a real system it would top the level up to the point where it seals itself off.
Actually it's even easier to just lift the bottle to the surface very gradually watch it empty, let it dip back in so it stops emptying - and use your imagination.
In Practice:There are a few practicalities that you have to address to make it foolproof. When the tray empties the air has to have a wide clear path into the bottle... surface tension means it can't be too narrow.
Either: The neck has to be held at least 3mm above the tray bottom (you can do this by making a 'cradle' from another bottle base - much pierced)
OR The bottle must have two unequal nicks (sawcuts) in the edge of the neck, one 3mm long and the other 5mm long; OR two 3mm+ holes low & lower down in the neck - OR a 3mm edge nick plus a hole 3mm from the neck is easy and reliable. You can either accept a bit of spillage transferring full bottles or you can put the cap back on and remove it when it is in the tray.
Wider-necked bottles are more stable - with 5L bottles I leave the cap on and put a 5mm hole through cap and neck at opposite sides at different heights - then I pick full ones up using a finger and thumb to cover both holes until they are in the tray.
Cheers.