Are there standards or rules for condo association reserve funds?

Are there accounting or other professional group standards that deal with what items may be included in a condo association reserve fund and whether the funds may be expended for items not originally specified for inclusion in the fund?.  A corollary question is whether there are items that these groups recommend or require to be included?

Our reserve fund has been funded for many years based on original and updated reserve studies. We are now faced with an unanticipated expense arising out of unusual rainfall and are uncertain whether it may be or should be funded out of the existing reserves.