"My 11 year old female, spayed dog was laying peacefully on the floor. When I bent down to pet her, I discovered a puddle of liquid on the floor under her hindquarters. It did not smell of urine, but there was a very mild odor and it was clear. I lifted her tail to see where it could have come from and it seemed to come from her vagina. The opening seemed very expanded, but not dilated. Her appetite is good and her bowel functions are fine. Is this an age-related issue or something requiring immediate medical attention?"
As female dogs age, urinary incontinence can result, especially in spayed females, due to lack of the hormone estrogen. If your dog is leaking urine, this may be what you are seeing, although an examination by your veterinarian is still in order to confirm, as a concurrent urinary tract infection is possible.
In an age-related incontinent dog (versus a congenital problem), muscles and sphincters aren't as "tone" as they once were, and urine leaks a bit into the common vestibule area. The urine may pool there, causing a "dilated" appearance. This stalled urine can lead to localized infections and may ascend up into the bladder, causing a urinary tract infection. As the dog gets up/lays down, a small pool of urine may be released.
In addition to loss of tone in the urogenital system, diseases such as diabetes or kidney disease often lead to increased urination (and thirst), exacerbating the urine pooling and potential urinary tract infection problem.
I recommend making a geriatric exam appointment with your vet for a physical exam, to check the urine, and bloodwork to make sure that there aren't any other or additional disease issues to deal with. Your veterinarian may order additional screening or diagnostic tests.
Hopefully, this is a case of "simple" incontinence and can be managed with medication to help tone the muscles for better urinary control, such as phenylpropanolamine (PPA) and/or provide hormonal support (Incurin).
For more information, here is a good article from Washington State University Veterinary School:
Standard disclaimer: anytime that your pet is not well, not eating, can't urinate or defecate, is painful or "leaking" something, please call your veterinarian immediately. This FAQ is not meant to diagnose or treat your pet; this can only be done with physical examination and proper veterinary care.