[oil pan 4]

I don't know what you have planned but when I am on the road over a thousand miles from home purified tap water isn't an option.
Its nice to have, I use extra clean tap water when around home, because I can and I like to.
Since water injection is proven to clean out every thing in the intake and nearly every think in the combustion chamber anything tap water leaves behind will be a tiny fraction of what the water removed.
You can always add wind shield washer fluid for added cleaning power, a little methanol and soap goes a long way, seafoam is also a possibility.

I had the intake off my diesel a few days ago and it was perfectly clean.


Any filter is better than no filter. Running no filter on your water injection system can allow dirt in and jam open a solenoid and cause your water injection system to leak water into your engine when its not running.
Even if you have purified water you can always get dirt contamination during transfer.