You don't state what you're making the wine out of, but if it's a kit, racking from the primary to the secondary shouldn't leave more than 750 ml of liquid behind. Essentially, anything that will go up the tube should be transferred over.
This seems counter-intuitive because you want to get clear wine, right? But the finings will take care of clearing in the secondary.
Next, at filtering, you should have a pretty compact sediment bed, with perhaps another 750 ml of volume inaccessible--if it's more than that it might be helpful to analyse how your fining process is working.
With those two things out of the way, the eventual yield of a 6 US gallon (23 litre) starting volume wine kit is almost always between 28 and 28.5 bottles to account for racking and filtering losses. If you top up with water, you'll get dilution of flavours and alcohol content--almost certainly something you don't want!
I love filtering, and actually own five Mini Jet filters (long story) as well as a Super Jet and an industrial plate and frame job. Wine that sparkles like diamonds is really worth the bit of extra work for me.
Hope this helps out.