Emptying a pool is not to be done without prior consideration. A considerable amount of damage can be caused by leaving a pool empty. Inground pools are like a large bath tub in the ground. When we get heavy or continuous rain for a day or two the soil can become quite water logged. If it wasn’t for the weight of the water in your pool, the entire pool can float. It is not uncommon for a concrete pool to lift up to 1/2 a metre out of the ground as a result. To alleviate this your pool has a pit in the deep end. This usually covered pit contains a spring release valve designed to allow water from the soil into your pool if the outside pressure is higher than the inside pressure. If a pool is to be left empty the valve is often completely removed so water can flow from the soil in and out of the pool as necessary. Fibreglass pools are easily broken and even more easily damaged if left empty. In above ground pools it is the water pressure which holds the liner in position. If you empty the pool you will have to ensure the liner is flat and smooth again before and during filling and that the sand beneath the liner is still flat and level otherwise you may end up with creases, wrinkles or tears in the liner.
The reason that you see local council swimming pools empty is because they have a special drainage system and sump pumps that remove water from the ground below them to ensure no damage occurs.
Due to the associated risks many companies will not empty pools unless absolutely necessary. Apart from resurfacing or other major pool rectification work there is usually no need to empty a pool. Algae or staining are the result of incorrect water balance and can be often cleared by correcting the water chemistry.