Document the loss
When it is safe, photograph affected areas and keep records of communications, invoices and work performed.
Describe the cause accurately
A sudden plumbing failure, gradual leak and storm-related intrusion may be treated differently under a policy. Do not guess about coverage; report the facts you know.
Ask restoration providers for documentation
If you hire a contractor, ask what documentation they provide for the work and keep copies for your records.
Keep a parallel homeowner file
Do not rely on one contractor or insurer to be the only keeper of the record. When safe, retain your own photos, estimates, signed authorizations, drying or moisture documentation supplied to you, invoices and relevant communications. EPA flood guidance also recommends contacting the insurer and taking pictures before cleanup where circumstances allow.