"Do you know about how much per liter?? I'm thinking maybe drops per liter???"
Much less than that. In fact, I try to see how small of a dot of Dawn detergent I can get. A
drop the size of this "O" is perfect for a one-gallon (milk) jug I use for watering.
The only time I don't run a drop of Dawn into my water is when I'm flushing. Remember that
old commercial on TV where they drop one drop of detergent into a greasy pot and all the grease runs for the hills?
Dawn makes water a lot more wetter, if that makes sense.
If you want organic, buy some Yucca Extract. It's the same stuff used in Advanced Nutrient's Organic Wet Betty. Personally, I just use name brand dish soap that has no phosphorus. Normally Dawn, because it's what I usually have on hand anyway, but Ivory is probably better.
Be careful with the dish detergents and shampoos -- you're much safer using a wetting agent specifically formulated for horticultural use.
Even though all of the above are classified under the broader heading of "soaps" there are some significant differences in the formulations. Dish detergents are generally anionic, which means that they carry a negative charge. They can be fast wetters, but also carry the potential for phytotoxicity. (They can also do nasty stuff to soil structure over time.) If you want to stick with dish detergents or shampoos, use CAREFULLY and SPARINGLY!
Non-ionic wetting agents formulated for horticultural use are really your best bet. They have very little potential for burn and are made specifically for use in growing substrates, so they'll give you better and more consistent performance. They may be a little more expensive than Dawn, but are better in the long run for the overall health and safety of your crop.
***FULL DISCLOSURE*** I work for a manufacturer of wetting agents for the professional turf and horticulture markets. That being said, I'm not here to sell you anything -- just trying to offer some good professional advice. Take it for what it's worth.