Blowing out water lines?

First a disclaimer as this is only my opinion and not intended to get anyone's shorts in a knot if they don't agree. :W

If one finds that emptying the water heater tank (6 to 10 gals) and a partially filled fresh water holding tank (say 10 to 15 gals) before towing is enough to make a difference when towing then IMO they're already towing way to close (or perhaps over) the limits of their vehicle. After all, we're talking perhaps 200 lbs of water and even for a trailer weighing a mere 4000 lbs that 200 lbs only represents 5% of the trailer's overall gross weight. In my case, I do tow within capacity of the vehicle and after an initial sanitizing in the spring (which I'm about to do today) I fill the water heater tank, half fill the fresh water tank, pressurize the trailer's water system, and leave it that way for the entire season, only fully purging it of water during my winterizing process. IMO there's just no reason not to and doing so allows us to use the system anywhere we want at any time, whether actually camping or not.

When breaking camp, I open the low point drains and faucets. I have a butterfly valve on the WH that I open so that it drains. When we get home, the lines are empty and the WH has sloshed out the calcification in the bottom of the tank, or at least some of it.
I only blow out the lines for freezing temps.
Never have worried about bacteria, mold, etc. in the lines. I do sanitize the FW tank before use, if it's been sitting for a couple weeks or so.

I always drain the hot water tank before travelling, towing with a 50 year old '65 Chevy van is very weight sensitive. Plus, 6 gallons of water adds 50 pounds of weight to haul around. Actually, all water tanks are empty when we tow.

Always winterize by blowing out system, quicker, easier, cheaper than antifreeze that makes water taste bad in the spring. done this since late '80's, never had a busted water line

Use treated city water and leave it in. I always handle it almost the exact opposite from how you describe. When I leave too go home I make sure my water system is completely filled for storage. Since you CANNOT dry out your entire system it's much better to have treated water instead of a warm, damp empty space in which bacteria, mould etc. can find a home.

Once season starts, I never drain. However, we rarely if ever drink from the faucet. Cleaning and showers only...

We only blow-out our water lines when camping in very low temperatures. The BLOW OUT method is very quick for us us if we feel like the low temps may do some harm to us over night. We can then re-fill the tanks the next day and continue on...

We also very seldom use our fresh water for consumption. We always have a couple of same brand bottled water with us to get the same great bean coffee taste when we grind and brew our own fresh made bean coffee all the time. We use this water for drinking and cooking with.

The campground and fresh water tanks are only used for washing dishes, taking showers, and flushing the pots etc... As said in a similar post up the thread here I also may get to squirt a squirrel too with the camp ground water haha...

Roy Ken

We only blow-out our water lines when camping in very low temperatures. The BLOW OUT method is very quick for us us if we feel like the low temps may do some harm to us over night. We can then re-fill the tanks the next day and continue on...

I suspect there is actually more chance for bacterial growth in drained untreated lines (moisture and air). I do not let my water system sit unused without chlorinated water in the tank and lines. You did not specify if the water in the system is chlorinated, but if treated IMHO it wouldn't matter if the lines were drained or not.
Since you are concerned with water quality and safety as opposed to freezing, I will add that I sanitize each spring at 50ppm for several hours, and after flushing, treat the tank water with 2-4ppm chlorine for drinking the rest of the season. If not used for more than 30 days or so I will drain and refill the system with fresh treated water.

I never drain my water heater or piping once the season starts.
I am using chlorinated city water and I go out every 2 weeks or so.
I see it as additional work. However if you are on a well or have the RV sitting idle for long periods. Draining maybe beneficial

I drain in the fall, hit the bypass for the water heater, pull the plug. (Mine does not have an electric element). Then I blow out the lines and suck in a little antifreeze. Fill the traps too. When it's finally above freezing for a week here all week. (So far, no joy) I Sanitize and fill the system. I don't drain it again until fall. I keep it full of water in the yard, as a power outage or two have caught me in the past and at least I can still have water/shower. (On a well). I don't travel with that water typically. (Weight)

I don't think you harmed anything... just a lot of extra work.