What detail do you need? It’s really easy and you can make use of a lot’s of components (maybe already in your drawer 
?)
- esp82xx, esp32 or a raspberry pi pico for the
of operation - 12V DC PSU (or something else
) - Valves, for example 12V DC (or again, something else
) - Some flow meter if you wanna know the amount of water (specially useful if you have alternating pressure on the system - for example because of using a tank which stores rainwater
) - some relays (which fit your valves, typically all AC/DC ones will do or maybe some solid state ones
) - DC-DC buck converter to power the esp/pipico from your PSU
Well, that was easy an cheap. I just upcycled 
some pastic container (~5L) for that task and installed is as a cover like seen in the picture 
works 
since ages 