The water jug

Every morning I fill a two-litre jug and put it on the table. My glass holds a quarter of a litre, so eight glasses empty the jug. This is just my jug, not a rule: how much water a person should drink depends on the person and on the day.

Jug: $2000$ mL. Glass: $250$ mL. So $2000÷250=8$ glasses. (Just my jug, not a rule.)

Jug $J=2000$, glass $g=250$ (mL): $J=8g$.

By lunch I had drunk three glasses, so three eighths of the jug was gone: seven hundred and fifty millilitres. Five glasses were left.

By lunch, $3$ glasses: $3\times 250=750$ mL, which is $\frac{3}{8}$ of the jug. Left: $8-3=5$ glasses.

Lunch: $3g=750$, which is $\frac{3}{8}J$.

In the afternoon it was hot and I drank four more. That made seven, and a quarter of a litre was left at the bottom of the jug.

In the afternoon, $4$ more: $3+4=7$ glasses, and $2000-7\times 250=250$ mL left.

Afternoon: $3g+4g=7g$, left $J-7g=g$.

I was about to drink that too, but the plant on the windowsill looked thirsty, so I gave it the last glass. Eight glasses left the jug: seven went into me and one into the plant. The plant drank an eighth of the water and looked very pleased.

The last glass went to the plant: me $\frac{7}{8}$, plant $\frac{1}{8}$, and $\frac{7}{8}+\frac{1}{8}=1$.

Me $\frac{7}{8}$, plant $\frac{1}{8}$; $\frac{7}{8}+\frac{1}{8}=1$.