If the hot water has a metallic taste to it then your water heater is probably close to breaking down. You should definitely try to replace your hot water heater as soon as possible and not use your water heater until you do so. Having a faulty water heater can be very dangerous. If you suspect that your water heater is failing, then you should not use it until it's fixed or replaced. Here is a list of signs of a faulty water heater in case you need it.