Holistic FLUTD Care can be accomplished in the home by acidifying the diet and increasing fluid intake. For emergency hydration, keep an electrolyte solution or instant for reconstitution on hand.
The first time a cat has this, it is very nerve wracking for the owner, as the cat is so ill by the time it sees the veterinarian. The second time it happens, the owner will wonder if there is something else that can be done. This page shows you what you can do.
Add some sea salt to the food. I suggest a few grains (by hand - not much!) on wet food. The purpose is to make your cat a little thirsty, but not to "season" the food.
Add a touch of vinegar to the water. Some malt, or cider, vinegar added to the water, will accomplish a more acidic urine. This discourages the formation of calcite deposits (stones or crystals).
If your cat stops drinking, s/he is in grave danger. Force some electrolyte solution into them using your medication syringe from your first aid kit, and get your cat to the vet. If the kidneys shut down, your cat may die.
Prevention
Keep the diet low in minerals. Magnesium and Calcium are the most obvious, but there are other minerals that may be involved. Watch the "ash content" of foods.
Adding Tinkle Tonic or another urinary tract supplement, is advisable for a cat that has had 2 or more urinary tract disorders.
Your cat may have to be retrained to the litter box after it recovers. You will have to deodorize, since it is likely that your cat associated the litter box with the pain of urination and stopped using it.