∵ An average demand of water = 33,000 litres
∴ Demand of water last for 50 days
= 33,000 × 50 litres
= 16,50,000 litres
Again, increase average demand of water = 37,000 litres
∴ Demand of water, last for 35 days
= 37,000 × 35 litres
= 12,95,000 litres
Now, demand of water, start for 15 days
= (1650000 – 1295000) litres
= 355000 litres
∴ Average demand of water
==23666.66 litres
Hence, minimum water should be used daily last 50 days = 23666.66 litres.