Will cat 6 will work if I pull it through old copper water piping?

Should work but check there's no water in them. See a retailer site for differences between Cat 5 and 6 (I suspect they are just quality levels so the plugs would be the same).

Andy,

Mainly, the tubes where you are putting the Cat6 cables shouldn´t be a problem at all. There are some considerations about Cat5 and Cat6 cables, HOWEVER, i sincerely don´t think that it should be something you are planning to take care.

Look, usually Cat5e should have as better quality issues and performance of cat6 to most applications. If you are looking for 1 GB networks, which most of new NICs are intended to be used, AND if you are talking about home networks, keep your money and use cat5e. Don´t hesistate at all.

Cat6 are mainly used for higher speeds and higher needs. In fact, I did a consultancy to a Brazilian datacenter which uses cat6, and they said that their needs could be achieved with cat5e, but regarding international standards and other things they decided to use cat6.

Everything on cat6 are expensivier than cat5. I personally use cat5e at home and office and can handle GB speeds with no problem.

Lets go back to your old pipes. Regardless of where you are, there are some international standards with obligates the installer to have all water plumbing really grounded. I don´t think that you may experience any problems. Before doing anything, make sure you don´t have any voltage running on this pipes. Could harm you. Old installations may have problems, but this shouldn´t be your problem.

Remember only to find out where this plumbing are running, since you may encounter some interference IF this pipes run real close to some lightings.

Anyway, I can tell you that you may use either cat5 or 6 with that tubing. Remember: no water inside the tubes.

REGARDING FIHART ANSWER:
We can say that the quality are just as good. Indeed it has nothing to do with quality itself. The cables are completely different. Different wire sizes, different reinforcement, cat6 has an internal "septo" which leads all 4 pairs totally separetad and OF COURSE, you can´t plug or insert a cat6 cable into a cat5 connector. Why: it does not fit! The RJ45 connection for routers, switchs and other stuff are the same, but the other part of the connector are not the same. Nor the prices!

Keep your cat5e and enjoy a dinner with friends with the rest of your money.

Hope this help.

LUIS

While luiscloss makes many valid points, I found relatively inexpensive CAT6 stuff at monoprice.com and wired my whole house with CAT6 rather than CAT5e. I did this because I wanted to future proof my home. While CAT5e may allow gigabit communication, when 10 or 100Gb comes around it may not support this. At monoprice, 1000 feet of CAT5e UTP rated at 350MHz is around $65 while CAT6 rated at 550MHz is just under $100. This should be a consideration as CAT5e may be fine now but what about later down the road?

* * * VERY IMPORTANT * * *
Whichever cabling you go with there is an important bit luiscloss forgot to mention: Make sure you buy the appropriate fittings
for the type of cable you buy. Even in CAT5e or CAT6 there are solid core cables and stranded cables. Each requires different fittings so make sure you by the right kind. And though it is not necessary, boots (those little covers that bridge the area between the connector and the cable) are good to have also.

Major,

Thanks for your reply. Its always pretty to receive some good comments.
But do not forget, this was on my original email:
The cables are completely different. Different wire sizes, different reinforcement, cat6 has an internal "septo" which leads all 4 pairs totally separetad and
OF COURSE, you can´t plug or insert a cat6 cable into a cat5 connector. Why: it does not fit!

Also, it is more than obvious that cables are getting cheaper and cheaper. Thats true! I personally dont like the prices here in Brazil. If you pick your example, we are talking about 40% price difference. It may not be very much for small instalations, but really expensive when talking about big project.

In fact, I do agree that when we will start (hopefully soon) to have 10GB and 100GB speeds the cables might be a problem. But dont forget to mention that today in most cases the bottleneck will be harddrive access time or machines internal bus speed. I personally dont like the boots, just because it makes difficult to manipulate the cables on patch panels (but you will not manipulate much anyway!).

Well, I still would go with cat5 and have that dinner! Take into consideration that most applications will be wireless in a near future, since this is also a tendency. Dont forget this!!! Today its not very fast, even running 802.11n.

Bye. Have fun. Cable or Dinner, its up to you!

Sorry for any confusion but you did not address what I was getting to. You are correct that the connectors for CAT5 and CAT6 are different but that is not what I was referring to. What I was referring to are the differences within CAT5 or CAT6 themselves. You can buy CAT5e that is stranded or CAT5e that is solid core. The connectors for these two cable types even within CAT5 are different. Same for CAT6. The point is to get the right connectors for the type of cable (stranded or solid) not grade (CAT5 or CAT6). I was making an additional point to yours. I hope that clears up what I was saying!

Its fine mate. As I told, its always good to receive good comments. Some comments I saw, werent really good in other posts. People sometimes take other people time to respond rabish. Take care.

It's all good, I was not clear enough and so it was good to elaborate on what I meant. Question for OP though....why do you need to run the cable through copper? Electrical conduit would be better, or none at all. I don't think I would choose to run any cable through a conductive material, if I had a choice that is.