DAY-TRIP WATER BOTTLE — ORIGINAL PACKING RECORD
Approximate plain-water mass; no personal drinking target.

TRIP / DATE / PEOPLE AND ACTUAL REQUIREMENTS:
BOTTLE / CAPACITY mL / BASIS OF CAPACITY FIGURE:
EMPTY MASS g / LID AND ACCESSORIES INCLUDED / MEASURED OR STATED:
CHOSEN STARTING FILL mL / APPROXIMATE STARTING MASS kg:
APPROXIMATE MASS WHEN FULL kg / UNUSED CAPACITY mL:
STOP / LOCATION / HOURS / ACCESS / CONFIRMED DRINKING-WATER USE:
SOURCE / DATE CHECKED / FACTS STILL UNKNOWN:
ALLOWED CONTAINER / BAG / ENTRY AND RE-ENTRY RULE:
IF THAT STOP IS UNAVAILABLE / ALTERNATIVE TO VERIFY:
WHAT WAS ACTUALLY AVAILABLE ON THE DAY / CHANGE MADE:

FORMULAS
Starting kg ≈ (fill mL + empty g) / 1000
Full kg ≈ (capacity mL + empty g) / 1000
Unused mL = capacity - fill

FICTIONAL EXAMPLES
Small bottle, partly filled | 500 mL / 400 mL / 180 g | 0.580 kg | 0.680 kg | 100 mL
Large bottle, partly filled | 1,000 mL / 750 mL / 250 g | 1.000 kg | 1.250 kg | 250 mL
Empty bottle to fill later | 750 mL / 0 mL / 140 g | 0.140 kg | 0.890 kg | 750 mL

EIGHT CASES AND ANSWER NOTES
1. A bottle has 1,000 mL capacity, 750 mL starting water and 250 g empty mass. What are its three results?
About 1.000 kg starting; 1.250 kg full; 250 mL unused capacity.
Add container mass to water mass, then divide by 1,000. Capacity minus actual fill gives room left, not a drinking quota.

2. A 500 mL bottle starts with 400 mL and weighs 180 g empty. Is 0.400 kg the whole packed mass?
No. The starting carried mass is about 0.580 kg.
The water contributes about 400 g and the container contributes 180 g. Counting only water omits the bottle and included lid.

3. A 750 mL bottle has zero starting water and 140 g empty mass. Does a valid result prove the trip supply is adequate?
No. The mass is about 0.140 kg, but access remains a separate question.
Zero is a legitimate known fill amount. The calculation cannot establish suitable supply, later station availability or personal requirements.

4. The empty mass is unknown. Should you enter zero to get a result?
No. Obtain or identify a usable mass figure first.
Zero asserts no container mass. A blank unknown must not silently become zero; note whether the figure is measured or stated.

5. Starting fill is entered as 800 mL for a 500 mL bottle. What should happen?
The calculator rejects the entry.
One bottle’s starting contents must fit its stated capacity. Do not clamp 800 to 500 or reinterpret it as several refill events.

6. The fictional 500 mL and 1,000 mL bottles above are packed together. What is the starting mass?
About 1.580 kg.
Add 0.580 and 1.000 kg, including both containers. The total 1,150 mL of starting water alone is not the complete mass.

7. A map shows a tap near the event, but drinking-water use and opening hours are unknown. Is the refill confirmed?
No. Keep the missing facts visible and verify an alternative.
Proximity and a map icon do not establish suitable drinking water or usable access on the day.

8. Unused capacity is 250 mL. Is that an instruction to drink another 250 mL?
No. It describes space in this bottle.
Packing capacity, drinking history and personal fluid needs are different questions. The planner does not supply a health target.

SOURCES
https://www.usgs.gov/water-science-school/science/water-density
https://www.nhs.uk/live-well/eat-well/food-guidelines-and-food-labels/water-drinks-nutrition/
https://www.nps.gov/articles/10essentials.htm