The innocent homeowner understandably expects the HOA to pay for repairs to his condo since the water intrusion came through a roof or water or sewer line that the HOA is responsible for maintaining.
Yes, a condo association is typically responsible for maintaining and repairing the roof and common water and sewer lines that serve more than one unit. But as long as the association fulfills its duty to make repairs in a timely and non-negligent manner, it is generally not responsible for damage to interiors caused by the occasional leak or back-up (unless there is insurance coverage, which really complicates the analysis).
The association might be liable, however, if it failed to timely repair a known waterline leak and the delay, rather than the original leak, was responsible for the damage.
Your question requires an analysis of what your HOA’s duty is with respect to the irrigation system and whether it was negligent in fulfilling its duty. If the HOA’s board of directors has a plan in place for the gradual replacement of system components as they wear out and performs repairs promptly when it is notified of a problem, then there probably is no negligence, and hence, no liability on behalf of the HOA.
I understand your frustration, but it sounds like this might be one of those “act of God” cases that many homeowners’ insurance policies don’t cover. I would check with your carrier and ask them to point you to the section in your policy that states there is a coverage exception for the damage you have suffered, but I will warn you that certain types of flood damage are often excluded from homeowners’ policies.