Total liters of water needed = number of attendee x water consumption/attendee
where
number of attendee = 7000 attendee
water consumption/attendee = 0.5litre of water/attendee
total = 7000 x 0.5 litre
= 3500 litres
computing the water requirement per 200 litre container
water requirement in the event = 3500 litres/200 litre /container
= 17.5 containers
The water requirement in the event at the arena of 7000 attendees is 17.5 containers.