Hi i am gathering you mean a Micro chip?
In 8 years of Vet practice the only problem i ever saw with the insertion of a microchip is they CAN sometimes migrate. Which means they can travel around the body but only through the skin layers. It will cause no harm to your pet whatsoever, it just can be harder to find when scanning, for this reasin the whole body will be scanned. The chip is made of silicone and will not have a reaction it unless a bacteria was introduced with the chip when it was inserted, which i have also never seen.
In Australia we tattoo the ears whilst the animal is under a GA with an "M" symbol in the right ear, this indicates the cat or dog has been microchipped.
Your cat can go in water as it is generally inserted under the skin at the back of the neckand the hole will heal over in a few days, you wont even see it. It will cause your cat no pain or harm and he wont even know that it has been done when woken
A specially designed scanner is used to identify the chip which has a long number on it in which are then linked to your details. Only Vets and municipals have the authority to get your details upon scanning.
It is not a tracking device in which alot of people think it is, it is only best when people take the cat into the vet ect to have the animal scanned should they find you. IF someone decides to keep your cat unfotunatley there is no way of finding him if they dont do the right thing and have him scanned.
The beauty about the tattoo is if your cat goes missing and so does his ID collar then the cat is still easily identified as having a micro chip.
It is the most efficient safest way to identify your pet
GO for it!! You will not regret it.