1999 Sundancer 310 V drive tap water question-it's hot on cold for short period

[Homelite]

Help,
On my said boat that I just bought over the winter, I get this condition when turning on the cold water. It is hot for about 1/2 gal of water. Do I have a bad check valve somewhere? Is this normal? Mkesa you waste water brushing teeth or something where you want cold water!

Thanks in advance

 

[KP49]

There should be a check valve on the inlet of the water heater to prevent backflow of hot water. The newer ones its in the fitting that screwed into water heater, on my older boats it was an inline check valve.