Vomiting Cats

Question
My cats have been vomiting on and off for about the past month.  I have two indoor cats, siblings, about 14 months old.  It started out with just one vomiting maybe once a week, then the other cat started doing the same.  Now, for the past week they have both been vomiting nearly every time they eat.  I thought it might be hairballs, but I only found hair one time.  All the other times it has been just the food they are eating that comes back up.  I have not changed their food.  I feed them Purina Kitten Chow twice a day.  Yesterday morning they ate and then vomited that afternoon, so I didn't feed them yesterday evening.  I also didn't feed them this morning and I may not feed them this evening because there was still some vomit this morning.  It was mostly water with very little solid in it.  Also, I haven't noticed any worms in their vomit or stools.  They aren't lethargic and seem perfectly healthy except for the vomiting.  What could be the problem and am I doing the right thing by not feeding them for 24 hours or so to give their tummies a rest?

Answer
Even though you do not see any worms does not mean they do not have any.  I would recommend a stool sample be taken to the vet to check as well as a dewormer be given.  

Yes you can fast them for 24 hours, but I doubt this will solve the problem as it has been going on for awhile.

In addition, I would switch them to an adult food beings that they are over a year old.  I would recommend a more natural diet than Purina...visit the pet store and look into foods such as Nutro Natural Complete, Prairie, Innova, Eagle Pack, Precise, Wellness, Natural Balance...try to avoid by-products, dyes, preservatives and artificial colors...ideally meat as the first ingredient is a better food.

You can also give them plain yogurt to try to help increase the good bacteria in their intestinal tract.

And if they are continuing to vomit, then you should have your vet take a look at them as they might need blood work or x-rays.