Food-grade polyethylene, the same stuff used to make plastic food containers like tupperware etc, and considered the safest form of plastic. Has added UV stabilizers to prevent the plastic breaking down outside and plastic softeners to make it flexible. BPA softeners may be used (I never could get a clear answer on that from any manufacturer).
At the drinking end, I have problems with this option. Plastic softeners like BPA are not what you want in your child’s tummy as the tank materials go though their inevitable off-gassing process. Softened plastics are also heavily associated with endocrine disruptors. These disruptions can cause cancerous tumors, birth defects, and other developmental disorders. Also, being outside, these tanks break down over time, regardless of the UV stabilizers.
Plastics are, as I’m sure you know, made from oil – which isn’t that great. Their embodied energy during production is pretty high too. After their service life, due to the UV degradation, they’re not considered recyclable at all. Which again ups their embodied energy.
Dead easy. All that’s required really is a stabilized flat spot. Because plastic tanks have a small amount of flex in them, they’re a bit more forgiving than other materials when it comes to installing. These types of tanks come in a wide range of sizes and shapes, which may aid installation.
Plastic tanks are a cheap option.
The toxicity and embodied energy didn’t make this option attractive at all, despite it’s price tag. Would potentially also melt in a fire accident, causing us to have no water. Not good. .
Made of concrete with steel reinforcing. Some times, Flyash is mixed with concrete to make it stronger. Concrete’s other components are sand, gravel, lime and water.
Not bad at all, as far as we can tell. Concrete tanks have historically been considered to produce superior quality drinking water because the great thermal mass of the tank provides a stable water temperature. This means less warm spots, and therefore less algal blooms. It is also often commented that concrete tank water has a nicer taste. This might be because of the various minerals leaching from the cement tank into the water. There are various reports about fly ash toxicity that made us wonder about it’s health effects when included in concrete, however.
Not so good. High embodied energy (about the same as a plastic tank for the same size). There’s also ethical questions about the sourcing of sand, as much sand mining happens in environmentally sensitive areas. Not recyclable, which means no chance of off-setting your guilt about the embodied energy. A well made concrete tank should last a very long time, however, which is a plus.
More complicated than a simple delivery. Requires a crew to come out, prep site and pour tank. Tank pad must be very well made and stable, or tank may crack. Some logistics to consider with access for concrete truck to tank site, weather, and so on.
Expensive when compared with Plastic Tanks.
Better than the options containing plastics, but still some toxicity questions. The non-recyclability also made it hard to get excited about this option.
Stainless steel, which is iron with added chromium and/or nickel.
Stainless steel is considered to be very safe and preferable for many applications, hence its use in surgical equipment, catering, drink bottles and so on. As far as we could tell, if you don’t heat it up or ingest shavings of it, it’s pretty much inert.
High embodied energy in production, but 100% recyclable. Completely and utterly. Because of its high value, the chances of the stainless steel having had multiple lives previous to its incarnation as a water tank are also high. Should last a lifetime.
Relatively easy, with good solid pad prepared - a simple operation of delivery and placement.
Expensive upfront, but when its all said and done, worth it. Very low toxicity means excellent and safe drinking water, and in 70 years time our grandchildren can use the steel for something else (or cash it in).