Brita Filter?

Most homes will have copper piping to transfer water, since it is anti corrosive by nature. But the RO/DI units themselves will be after the piping, which is where some 99% of the contaminants will be filtered out, including the copper traces. The tubing in the RO/DI units are made of plastic composite that does not leach into the water.
Another issue that usually gets forgotten about regarding distilled water is that it is extremely inert as far as buffering capacity goes and will drop the KH value in the tank if a buffer is not added. Not meaning to argue or anything, just wanted to clarify.

 

You can get a really good 5 or 6 stage system off ebay for about $150. And if you don't want to make a permanent install, you can get a garden hose adapter for the input feed, like sostoudt mentioned. Getting one was one of the smartest investments that I have made. Not only do my tanks get pure water, I know when I drink the water myself, I am getting clean water too. Using a phosphate sponge will only remove the phosphates, it won't reduce the other contaminants, like heavy metals and sediments. If you saw what the TFC membrane pulls out of the water after a few months worth of use, you would NEVER drink tap water again, nor would you want to add tap water into your tanks either.