my german short hair pointer,...

Question
my german short hair pointer, age 12, suddenly urinated on the rug just
prior to walkies; also: he has been unable (or unwilling) to hold his
urine until we get out to the street, sometimes walking and urinating at
the same time.  He is healthy and full of energy with a good appetite but
a seemingly insatiable need for water.  

Answer
HI there!  I would definately have him checked for diabetis.  Older pets have the tendancy to display the symptoms you have described when diabetis is present.  To test the glucose level, your veterinarian will just take a tiny bit of blood and test it in the glucometer...just as we humans test our glucose levels.  It only takes about five minutes and ranges between $10-$15.
He may also just be experiencing the loss of bladder control, as some animals do in older age.  There are medications that can help this and some pet owners actually purchase diapers for this situation.
Either way, your best bet would be to have your veterinarian physically examine him, just to be sure that there are no health problems that are causing this, and if there are, that they are promptly treated.
I hope this has been helpful and please let me know how he does.
Give him some kisses for me,
Hilary