Moved to the correct forum.
To answer your question, your best bet is to experiment a bit. The ratio to use depends on your air temperature, humidity, palette composition, and paint that you're using.
Also, Les Bursley's wash recipe is available here:
https://www.dakkadakka.com/dakkaforum/posts/list/261541.page
It's solid advice, and would be a great place to start.