Fresh water tank life expectancy
 

Is the liner for the fresh water tank infinitely viable or is it something that should be replaced after some 47 years when refreshing things that matter? If it were clear or translucent plastic you could at least see living critters of microscopic origins resembling a bachelors refrigerator. The unknown layers of scum left over from years of questionable water sources has me thinking to error on the side of safety. Flushing with water/bleach and letting the mixture simmer is doable but does the plastic internal liner have a life cycle that must be considered?

This system is a hand pump pressure type and if changed to a new tank would it need to go to a power pump delivery because of plastic tank power pump compatibility? The unit this is in is a 1971 Jo Bud 16' that is Hi Lo twin brother from a different mother and is hard to tell it isn't a Hi Lo brand.

Fresh water tank
 

I would modernize and put in a new system. That way you won't take a chance on getting sick. Not an expert.

The water is fine for a shower and washing dishes, do not drink it. Filter it or replace the tank. A Berkey filter system is a good option. I use one, the Travel version, does not mean travel though, and I dont have to worry where I get water from.
Plastics will break down over time, a few years, and be toxic. I toss bicycle type bottles after more than 5 years, after ten you can taste the petroleum.
The plastics leach out the toxins into your water.
I would keep the tank and filter for consumption.

Marininn, good points on plastic leaching. I will be removing the original metal with a hand pressure pump system and going to the blue plastic 7 gallon containers available at every Walmart and stores like that. They have a port where the reversible spigot is that a hose going to a pump can be used instead. Placement has yet to be determined but closer to the wheel well may be a better weight balance too.

Hose water might be worse…
Use a vinyl tube not a hose. or that copper is good forever.
That is a nice tank, is it a pressurized tank system where the tank is pressurized to provide flow? I see flange fittings which suggest pressure.
I would just get the water tested first. It might be fine.
The tank is galvanized on the outside. Are you sure it has a liner?
Bite the bullet and get a square shape tank to fit in your space. Retrofitting bottles will not be a long term fix, I bet they leak at the caps. One drip per day will rot out the floor over time.

This looks similar to the water tank in my Hi-Lo What am I going to run into y removing it? Are there weld spots holding it in? Will I need to plug water lines to it? I want to change to a plastic water jug system under my sink.

O I see you said "hand pump"..
I have a metal tank out of a 1971 camper that was a pressurized one. All the fittings were welded threads in the tank, so the regular water tank fitting just screw into it the same as do a plastic water tank. To replace you may or may not can re-use the existing fittings, and you will need a water pump. The pump will pull from the lowest drain hole (threaded as mentioned) and the vent will be higher (lets air in as you pump water out).
Pretty easy job and if you do not know how to do it then this is a good project to learn by doing.
There is nothing welded that holds it in, just straps or bolts holding the feet to the wood floor.
And yes, you will need to hook up the water lines to the new tank. One line out. One line in, and one vent line. You can add two lines in if you want both gravity fill and screw-to-the-side of camper hose fill.
Good news is that water tanks do not bounce; the water keeps it from bouncing, so minimal needs to be done to keep the tank from bouncing down the road, but do secure it side to side and front to back well.