The act of topping up or adding more (usually gradually) to something that is running low; an addition or replenishment.
スープは煮詰まったので、継ぎ足しをしながら味を整えた。
The soup had reduced, so I adjusted the flavor while topping it up.
このつけ汁は長年の継ぎ足しで味が深くなっている。
This dipping sauce has deepened in flavor through years of continual topping up.
ボイラーの水は定期的に継ぎ足しが必要だ。
The boiler's water needs to be topped up periodically.