Jersey Water says we got through almost 5% of our overall stock last week, using a total of 159 million litres.
The surge in water use, to 23 million litres per day, came as the island, along with the rest of Europe, experienced an intense heatwave.
Jersey recorded its highest-ever temperature of 39.3°C on Thursday 25 June.
Despite the increased demand, the utility says reserves are on a par with what we would expect for the time of year, at 89%.
Mark Bowden, Head of Water Resilience and Emergency Planning, told Channel 103:
"The reserves are holding up quite well - pretty much bang on the ten-year average.
"This year, we had a very wet February, and that made our reserves hold up quite well. We had a bit of rain through May, so that gave us another little boost."
However, he has urged caution to get through the rest of the summer:
"We see those spikes - the use of hosepipes filling up paddling pools and watering gardens.
"Another warm spell could make quite a large dent."
Temperatures are predicted to rise again next week, to the high twenties or low thirties Celsius.
Mr Bowden said there is no need for any restrictions at this stage, but hot weather does put pressure on supplies.
Although we have another hot spell expected, senior forecaster Bryan de Gruchy says we're not approaching drought conditions:
"We did have 1.7mm of rain overnight on Monday.
"Before that, we had had 10 days without measurable rainfall, but we need 15 days without measurable rainfall to qualify as a drought."
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