Whanganui District Council's chief executive David Langford said civil defence personnel usually had other critical roles.
"When those people are responding to an emergency it takes away from the council's ability to perform its core functions so knowing that we are able to call on our neighbours for support is very reassuring," he said.
"In Whanganui, we're no strangers to responding to emergencies as was evidenced during the flooding in 2015. Neighbouring councils in the region have always been willing to lend support to one another and the charter has formalised that commitment."
Manley said the charter recognised that no council had significant reserve capacity for either staff or contractors.
The charter commits each council to provide resources to assist other councils with specific operational issues if they have the capability to do so along with when and how this would be delivered.
Although it doesn't describe the precise level of disruption needed before assistance is sought, it was understood that assistance would be offered when any council should experience a "high or extreme risk to their safe and effective function".
Those functions would include three waters services, solid waste, environmental health, building and animal control, cemetery services, public facilities and essential corporate services such as digital technology and computer network support.