Red-faced Dudley Council officials had to admit the gaffe at Stourbridge's Crystal Leisure Centre which has been closed since Saturday, just as children were going to be able to swim for free as part of the holidays.
The leisure pool, which has slides, a beach area, bubble seat, toddler slide and water feature, is set to reopen "later this week" according to Dudley Council, which runs the facility.
Dudley Council’s leisure chief is now offering an extra weekend of free swimming on Saturday, November 6 and Sunday, November 7 to "make up for it".
Councillor Simon Phipps, cabinet member responsible for leisure centres, said: "We apologise for any inconvenience the unexpected closure has caused this half term and we know families will have been disappointed.
"But we didn’t want children to miss out on their free swimming so I hope families will take up the extended offer in the first weekend of November.”
The leisure pool and 25 metre swimming pool had only been reopen to the public since August when it was unveiled after a renovation.
The wave machine was refurbished and the changing rooms were demolished and completely remodelled.
New visual effects made it look like there were fish in the sea in the leisure pool which is always popular with families.
The leisure pool and 25m pool were drained, repaired, cleaned and refilled, which made the draining by mistake all the more embarrassing for staff at the leisure centre.
Any youngster aged 16 and under who lives in Dudley borough is eligible to take advantage of the offer by registering online at freeswimindudley.co.uk.