Burrator Reservoir on the edge of Dartmoor is just 74.7 per cent full while at the same time last year it was 99.7 per cent full - and nearby Roadford is just 77 per cent full.
The reduced levels come after six months of exceptionally dry weather.
According to the Government's Centre for Hydrology and Ecology the South West has seen its lowest rainfall over 16 months since the drought year 1976, when a fierce drought affected much of Britain for months.
Terry Marsh, from the CEH, told The Guardian: "A dry April could lead to a significant deterioration in the resources outlook, so we need to keep a careful eye on things over the next few weeks."
England saw its driest March in 50 years.
A South West Water spokesman said: “Total storage is currently lower than the same period in 1995, which is a situation we have experienced four times in the last 14 years, but there has been no need for water restrictions in any of those years due to a number of positive long-term developments.
“These include our industry-leading record on tackling leakage – reduced by 60 percent since 1989 – and demand for water falling due to nearly 70 percent of households now being metered.
“We have also upgraded our distribution network so it is easier to move water around the network and improved the efficiency of our works so we use less water in our treatment processes.”
South West Water's figures show that Burrator's levels are significantly lower today than they were at the same point in 1995, a drought year, and the water company's other major reservoirs are also seeing reduced capacity. Colliford is 14 per cent down year on year and Wimbleball is 10 per cent down year on year.
Overall South West Water is storing 85.5 per cent of its capacity of water compared to 97.7 per cent at this time last year.
South West Water is taking water from rivers to top up its reservoir supplies.
The warm, dry weather is set to continue into May as a high-pressure system in the Atlantic is keeping rains away from the UK.
Jonathan Powell, senior forecaster at Positive Weather Solutions, told The Express: “Some places will inevitably see hosepipe bans at some point as there is no substantial rainfall on the way.”