I have no idea what this means, "100% tapas long as it is treated with prime or equivalent". Sorry...
Means that 100% tap water would be fine aslong as you are using Prime as your water conditioner ... Here is some of what it says on the bottle:
"Prime converts ammonia into a safe,non-toxic form....... Detoxifies nitrite and nitrate allowing the biofilter to more efficiently remove them "
So if you have trace amounts of ammonia and nitrate in you tap water using Prime will make it safe for the fish... You still might get a reading on your ammonia test showing the .5 you were getting from the tap but you will know it has been converted to a safer form.
To try this buy some Prime and test a sample of tap water... if it still shows the .5 ammonia add Prime to the sample and take another test of it after you add it... It may still show the .5 but it will be a safer form ....so knowing this anything over the .5 in your tank testing can be interperated as a rise in ammonia since you know it is always going to test at .5 because that is what your tap water tests at.
Hope you understand what I am getting at...harder to write things out sometimes than it is to just talk to someone face to face