From what I read about it, for three reasons: It's not entirely clear (some people/studies say it's fine, others say it's not) whether certain pathogens ca

From what I read about it, for three reasons: It's not entirely clear (some people/studies say it's fine, others say it's not) whether certain pathogens can end up in your vegetables this way and/or which vegetables would be fine and which wouldn't. I mean, some people do compost their own #2 and put it on their veggies and while it's been OK so far for many, I personally stay on the safer side of these things until desperate times call for such measures. Anything that has a root system that is able to reach the septic field's drain lines is potentially able to clog the holes. E.g. I tried raspberries in a planter on top of it for a while but even though I tried, I couldn't contain the roots and/or raspberries fall down and the seedlings grow in the grass. I ended up removing the whole thing just in case as septic drain field repairs are either expensive or a lot of work. Evaporation apparently plays some part in the effectiveness of the drain field (it doesn't just all drain out into the ground). Though I wonder, why plants taking up the water and evaporating it via their leaves wouldn't do the same thing, potentially even better through a larger surface area, so I guess it's mainly the first two points.