High-Density Polyethylene (HDPE) like those black poly pipe very commonly used now (and the tank) is safe for use. HDPE products are safe and are not known to transmit any chemicals into foods or drinks, making this plastic a low health risk variety, according to Chemical Safety Facts.

Stainless Steel also leach iron, chromium and nickel into water also but probably not considered as harmful also.

This leak can be treated and repaired. The concrete load also depends on the iron bar used.

You can google for video on how to repair the crack line. Plenty

Of course you'll never know unless you get the architect drawing

Looks like they designed the tank to be put on concrete slab. I'm sure that part of concrete is the strongest point. Probably got column to support it.

Dunno anything much about Penten.

Looks like your tank is poly material. Excerpt from Wiki:

Although HDPE pipe is often estimated to last 50 years, they are in fact more likely to have life expectancies of 100 years. PIPA (Plastics Industry Pipe Association) and the Plastic Pipe Institute (PPI) have written technical white papers on HDPE design life.

Note HDPE (high-density polyethylene).