feral cat unable to urinate

Question
Greetings.  I regularly feed a colony of feral cats (all spay or neutered).  I noticed 2 days ago that one of the older females was continuously squatting to urinate but not passing anything.  I made an effort to mix the canned food I fed her with some extra water which she took well.  The next day I observed her squatting and she had produced a small amount of urine in the grass....I dipped a white paper towel into to see if there was any blood...fortunately, there was no blood, just very dark urine.  Today she was ready and anxious to eat, did take additional liquid with her food but was observed squatting about 5 times in less than 1/2 hour with no result(just after eating so not much time for kidneys to produce.)  I don't know her age but do know that she has had at least 3 litters and was spayed over a year ago.  I just cannot afford to treat her at a veterinary hospital and  am wondering if there is anything I should try to do for her in terms of feeding,etc. which is my only means of intervention.  I don't want her to suffer or to go somewhere and die...I would rather take her to be humanely euthanized but, of course, don't want to "jump" the gun!  Any advice would be greatly appreciated.  
(I do give them grain free dry food and a variety of canned foods but know that other people in the area leave lots of lower quality dry food for them.)

Answer
Hi Meredith,

I would strongly suspect that she just has a urinary tract infection. This should be less expensive to treat than euthanasia (unless you were referring to relinquishment to animal control). Generally, I will just tell the vet I want to treat it as an infection without going into diagnostics, and see how she responds. Unfortunately, you won't be able to rid her of an infection without antibiotics, and those must be prescribed by a vet.

In my experience, grain-free foods prevent urinary tract crystals better than any other diet, strangely. I'm not exactly sure of the scientific reason behind that, but I have three males prone to blockages, and they are better managed on grain-free foods than on urinary tract diets. I think continuing to feed her grain-free is the best you can do in case she is having crystal problems.

I would encourage you to see if vets offer any discounts on rescue cats, or if they can refer you to a trap, neuter, return org (if you don't know of one) that might be able to arrange discounted services. Some even have a vet that oversees cases that will prescribe antibiotics for free.

Good luck!
Jessica