Is it bad to have water in your spinal cord?

No. Spinal cord and around it normally and is called cerebrospinal fluid csf.
Not Always. There are a number of conditions that may be termed 'water in my spinal cord' . Common finding is an enlarged central canal that is a normal variant and requires no treatment. True syringomyelia can be caused by a number of pathologies including hydrocephalus, chiari malformation and less commonly a tumor. I would recommend that you seek a referral to a neurosurgeon to get this sorted out.
Not necessarily. Water in the spinal cord is usually indicative of a "syrinx" which means there is a fluid collection in the spinal cord. The important part of a syrinx is to have an MRI if possible and an appointment with a neurologist or neurosurgeon to see if you have any symptoms attributable to the fluid in your spinal cord. These may occur from trauma, tumor, or present at birth.
Sometimes... Everyone has "water" in their heads and spine called cerebrospinal fluid. This fluid looks like water, is created in the brain and circulates around the brain and spinal cord, nourishing and protecting the central nervous system. Rarely, this fluid can enter the middle of the spinal cord; if the pressure rises enough it can cause spinal cord injury. Google "syringomyelia" for more information.
In it or around it? "water" ie cerebrospinal fluid (CSF) is a normal condition to have around the spinal cord. In fact not having CSF around the spinal cord may signal the presence of severe narrowing of the spinal canal, potentially a surgical condition. Water in the spinal cord as in in internal cavity (cyst or syrinx) is always abnormal. If you have fluid in your spinal cord see a neurosurgeon.