In my opinion, as an investment into future of the business, HACCP Certification today appears to be inadequate.
Historically speaking, the resultant was the emergence of several private and sectoral standards. Whereas IMO, ISO 22000 provides increased assurances to your consumers that the FSMS is supported by requirements of the standard (see requirements).
The difficulty is really not in the documentation if your Consultant is familiar with the requirements of ISO 22000 but rather in bringing your facility & process controls up to speed in meeting relevant conformity and compliance issues. For example, in HACCP, the flow diagrams I have seen to-date are generally kept very simple whereas in ISO 22000 you would need to demonstrate the composition of the "3-Legs" i.e. combination of control measures covering CCP, OPRP and PRP.
In other words, when your facility is subject to a 2nd or 3rd Party Audit, you can be assured that the product's credibility is enhanced. I hope to change your view on HACCP and move to ISO 22000 afterall I sincerely believe that the bottled water business will grow tremendously when the future of safe potable water is in danger.
Cheers!