You're right, my previous response about the 5000L tank price was incorrect. After re-checking the results from my PriceCheck search, I don't see any listings explicitly for a 5000L water storage tank. The largest vertical tank listed was 500L for R1966.50. For very large commercial-sized tanks over 5000L, your best option may be to contact suppliers directly. Apologies that I don't have more relevant options from my limited catalogue. Please let me know if you need any other assistance finding a suitable large water storage solution.
