Hydroponic plants are always grown in some form of container; in essence they are a container with water, and sometimes fancy tools like pumps. A lot of people grow small produce like lettuce in mason jars using the Kratky method, but most commonly plants are grown in plastic buckets, totes or buckets.
Keep It Food Safe
It needs to be food-safe, and yes this is important. Many people will use plastic containers but they are often unaware that overtime plastic degrades and can leach micro-particles and chemicals into the water, all of which will be absorbed by your plants as they grow (and subsequently eaten by you).
Plastic leaching these dangerous chemicals are even worse if you live in a hot environment, and if the plastic is exposed to heat at any time (such as at the store before you bought it). Furthermore, some plastics will react if exposed to certain products, especially if they are too alkaline or too acidic.
The wrong chemicals exposure can be dangerous. BPA and some phthalates are endocrine disruptors, mimicking natural hormones and causing a cascading number of different health problems such as infertility, obesity, breast cancer, prostate cancer, reproductive development, heart disease, diabetes… and more.
Honestly, just don’t risk it.
What Plastic Can I Use?
Find a container using Polyethylene Terephthalate (PET). Apparently PET is “biologically inert if ingested, is dermally safe during handling, and is not a hazard if inhaled“. PET wont degrade when in contact with food or beverages.
Polypropylene (PP) is another common used plastic; found in many food storage containers and microwave safe containers. This plastic can be heated safely, and it doesn’t react to liquids, acidity, or alkaline foods.
High-Density Polyethylene (HDPE) is often found as dairy containers (milk or butter), cereal box liners, and large food buckets. It doesn’t absorb liquid, and futhermore doesn’t leach chemicals into their contents.
What Plastics Should I Avoid
Recycled Plastics Any plastic that is recycled may not be food safe. I would avoid any recycled plastics for hydroponics.
A quote from the FDA describing the risks of recycled plastics:
1) that contaminants from the post consumer material may appear in the final food-contact product made from the recycled material, 2) that recycled post-consumer material not regulated for food-contact use may be incorporated into food-contact packaging, and 3) that adjuvants in the recycled plastic may not comply with the regulations for food-contact use.
PVC. Did I just say that right? Yep. A lot of DIY hydroponics use PVC pipes to store and run their hydroponic solutions, and even grow their plants. In it’s rigid form PVC is probably safe, however in its flexible it could be dangerous. To make it soft a plasticiser is added, often up to 40%! According to Choice Australia recent studies have raised concerns about the health risks.
Polycarbonate should be used with caution. Whilst a lot of food storage containers are made with this plastic, recent studies have suggested that polycarbonate can release bisphenol A (BPA) which can cause serious health problems.
Further information on types of plastic (and their numbering system) can be found here: https://www.chemicalsafetyfacts.org/types-plastic-food-packaging-safety-close-look/