Water help

[BFG Central]

I should imagine one is a header tank if you have an older gas central heating system with a copper tank.
The other one may be in place to provide pressure.
If you plan to use them as emergency water make sure its clean water.

DO NOT use the water from the one being as an expansion tank for your radiators as this will contain chemical. .

Its easy to work out if its good drinking water or not.
Just run the taps and see if they start filling up.