I'd quibble with your assertion about flex PVC not being food safe. Here is what FlexPVC says when asked that question. I don't know enough about how silicone tubing is made to say whether it would be similar.
I would like to understand which type of PVC would be recommended to safely grow edible plants. I have read that some types of PVC may not be safe for potable water? Thank you.
All rigid pvc pipe and fittings well sell (whether made in the USA or China) have an NSF61 rating for potable water. (Potable water is generally considered the highest standard and approved for human consumption.)
Rigid PVC pipe and fittings are 100% safe for food, water, human consumption, farming, livestock, etc. to the best of our knowledge and established science and standards.
Our Flexible pvc pipe has an NSF51 rating. Generally NSF51 is considered safe for delivery and processing of liquids (wine, beer, milk, etc) during production, however the rating for our flexible pvc pipe is for swimming pools. It would pass an NSF51 certification for food if submitted but since 95% of the people using the product are using it for non-food applications it's not worth the money ($250K and up) to get a separate certification. Furthermore the product would also comply with FDA recommendations. The FDA does not give certifications, it only lists approved and banned products and generally as long as you aren't using any banned products then the product is considered "compatible" with FDA standards.
The flexible pvc pipe can not get an NSF61 rating because if water sits in the pipe overnight, it will pickup a plastic taste and in order to get an NSF61 rating, it can't alter the taste (that's the only criteria our flexible pvc pipe can't meet.)
As for growing edible plants with pvc such as hydroponics, we know of thousands of customers who use it for just that purpose, some of them organic certified, so we feel confident it would have no detrimental affects on plants or food.
