Neutered male cats are prone to urinary crystals, and if the problem is not taken care of in a reasonable amount of time, the cat can die. A "blocked" cat suffers one of the most painful ailments a cat can suffer, as his body is being poisoned by urinary infection.
Many people do not recognize the signs until it is too late. If you notice your cat straining in the litter box, acting like it's constipated, there is a good chance it is beginning to block. If it starts soiling areas or urinating outside of the litter box, there is a problem. If it tries to urinate frequently, but nothing or just drops come out, it is preparing to block. The reason cats soil areas outside of their litter boxes is because they are associating the litter box with the pain of urination, and they reason that going in another area may lessen that pain.
In the beginning, crystals will cause the opening of the urethra to become blocked partially, so there still may be a trickle of urine. As the problem progresses, however, the trickle slows to a complete blockage. Sometimes the bladder ruptures. Generally, once a cat becomes totally blocked it takes three days to die and it's a horrible, painful death. They will begin crying in pain, and eventually the pain will put them into a coma. It is cruel to let a cat die that way.
Sometimes the cat can be catheterized and just the insertion of the catheter will enlarge the opening and allow urine to run freely again. But if measures aren't taken to prevent crystals from forming again, he will become blocked again. If catheterization doesn't work, surgery will have to be performed, which slits the penis and allows urine to flow. This surgery can cost upwards of a thousand dollars.
If you can't afford the surgery, it would be more humane to put him down before the agony becomes unbearable. Imagine yourself not being able to urinate for days.
Diet can control the amount of crystals in a cat's urine. Cheap foods found in supermarkets are full of dyes and are high in ash. Both can cause crystals to form. Check the labels for cat foods that say "for urinary cat health." Also, mixing canned wet food with the dry food is helpful, as the fluid in it helps move the fluids through the cat's body and out, before the urine can get highly concentrated and become crystallized. Don't give them cow's milk, because it is not a natural food for cats. Wet food and lots of water will help more than anything.
A better brand of food may cost a bit more, but it can save you hundreds of dollars for vet bills and save you large amounts of heartache.