How much water do you have to drink for it to be a problem (water intoxication)?

1-2 gallons; depends: Quickly drinking lots of water will lower one's blood sodium (salt) level, affecting the brain and heart. The exact amount of water needed to cause damage varies, depending mainly on one's body weight and amount of dehydration. Symptoms include confusion, dizziness, nausea, & seizures from brain swelling. Endurance athletes sweat away sodium, and should rehydrate gradually, with some electrolytes.

Depends: Based on average american diet, it would have to drink 10-12 liters of water to develop water intoxication. If you eat less (for example such an alcoholic who ingests primarily beer), the amount needed would be less. Symptoms are usually related to alterations in mentation.

Depends: It depends upon several things. If you are doing strenuous exercise or working in a hot environment then you will need more water. For most people drinking 6-8 8oz glasses of water a day is plenty. If you drink excessive water your kidneys can not process it and electrolytes get out of balance. This can be serious and cause the heart to get out of rhythm.