India's killer heatwave is leaving the country reeling from the worst drought in decades and a rural population struggling to survive. Relief is due with the arrival of the monsoon in mid-June, and because of the impending La Nina weather pattern, the forecast is for above-average rainfall. However WaterAid India's Head of Policy, Nitya Jacob, says groundwater levels are so depleted that even if a good monsoon comes in June -- and meteorologists predict there will be one that ends the drought -- it won't be enough.

"Even if the monsoon is good, it cannot compensate," Jacob told CNN. Central Water Commission data shows that India's major reservoirs are 79% empty, and 75% of India's basins are holding less water than the 10-year average. CNN Meteorologist, Michael Guy, says this is usually the hottest time for the subcontinent, but this year has seen an unprecedented spike in temperatures.

"India is currently in their summer or pre-monsoon season, which lasts from April to late May, or early June," says Guy. "This year we've seen temperatures range from the lower 40s to as high as 47?C or 116?Fahrenheit. For some, this is three to five degrees (Celsius) above normal." And critically, the past two monsoon seasons have seen below average rainfall. "This has had a huge impact on groundwater supplies," says Jacob.

The government estimates up to 330 million people could currently be affected by the dry climate conditions. "We are seeing that people don't even have enough water for drinking," says Jacob. In an open letter to India's Prime Minister Narendra Modi in April, more than 150 of India's activists and academics expressed their concern about the drought's impact on the rural population. "In areas where rains have failed, farmers who depend mainly on rainwater to irrigate their crops have no, or very low, crop yields," they wrote.

"Those who rely on irrigation are also affected, with groundwater sinking and streams and reservoirs drying up." The combination of heat with humidity makes India a global hot spot for heat-related illnesses and fatalities -- so far the government estimates more than 370 people have died. 2015's heatwave led to around 2,500 deaths in India, making it among the top five deadliest years in recorded history. "It was a wake-up call for us," said K. Dhananjaya Reddy, the director of disaster management in Andhra Pradesh, a state that saw more than 1,300 deaths in 2015.