Your lips can’t sweat, so I’m not sure you can take anything from this. Sweat from your head/face dripped onto your lips, sweat contains salt, thus you felt/tasted salt on your lips.
There are two factors at play, sweat concentration (how much salt you lose) and sweat rate (how much water you lose). Your concentration is relatively consistent (heat adaptation among other factors can alter this a bit). However, sweat rate is quite variable depending on various things, most notably effort and cooling.
You can trial and error to try and guess your salt/sodium loss, but really you’d need to get this tested to get it right.
Whether training indoors or out, I make a habit of jumping on the scale before and after. It’s a pretty good way to keep tabs on hydration (via weight and the scale also estimates water as a % of weight). Some of the weight is technically glycogen, but it’s still good to know how far down you are after a ride/race/training. For hard indoor sessions (always 68f or lower and with multiple fans), I’ll loose about a 1.5lbs per hour even when drinking a 24oz bottle about every 45 minutes. Outdoors in the TX summer heat, it’s not unusual to loose 8-10 lbs during a hard ride/race even when drinking ~2 liters per hour. I pretty much train/race with a hydration pack and 2-3 big bottles during the hot months to minimize stops. While I get a lot of crap for rocking the hydration pack on the road, I’m also not the one begging for a store stop every hour or imploding from dehydration.
Not enough to be honest but I don’t sweat much outside, particularly after my chemo ‘treatment’ 5 years ago. Last Tuesday’s paceline was what should have been a very comfortable 17.2deg and I was freezing. I probably only took a 1/4 of a bottle in 1h40 during the Paceline. For last night’s session (3x12mins at SS), I realised I forgot to refill my bottle and for 2h in 8.4deg C (what a difference a week makes) I only took sips in my three off intervals. On the trainer its hotter (usualy 20deg or more) and depending on the intensity I will get through a 750ml bottle in an hour.
These days, I’m drinking a 750ml bottle about every 90 mins, often 2 hrs in winter. Until I upped the amount of sodium I add, and started using it consistently, I was drinking that much every hour.
I need to try to get back to drinking that every hour again, or at least the first bottle, because I am definitely compensating (really thirsty and drinking a lot) the rest of the day, but with the consistent sodium, I at least don’t feel bad after the ride anymore.
Recently had a sweat test done to find that I am a very salty sweater. Also have done some weight tests before/after and I sweat about a liter per hour which I think is about in the middle. I try to drink every 12 minutes which typically will result in 750ml bottle every 1.5 hours. On hot days I will switch to a 1 liter bottle. I have also started adding sodium citrate to my bottles to try and get the sodium around 800-900 per bottle.
If it’s cool out, .5-.75mL/hr. When it’s warm, 1 liter/hr.
On the trainer, usually around .75-1mL/hr depending on intensity.
I aim to get most my general hydration for the day in by around 3-4 pm and drink a very small amount with dinner and a small sip after brushing my teeth before bed. Refraining from liquids later on has really helped minimize the chance I get up in the night to pee, and alternatively sleep better.