How to Drain a Swimming Pool

How to drain a swimming pool.

Before you drain a swimming pool, the first thing to consider is whether it is really necessary. Many repairs to the pool lining and/or tiles can be carried out by trained divers without needing to empty. However, a lot of structural damage can be done to the pool construction if this task is not carried out correctly.

There are occasions when the pool water will need to be emptied. An example would be if any broken glass somehow found its way into the pool water. Because glass is completely invisible when submerged in water, the entire pool contents would need to be emptied. Then, a thorough clean-up operation is carried out to ensure that all traces of glass have been removed.

Procedure for draining

  1. Carry out a suitable and sufficient risk assessment for this job before going ahead with anything. This risk assessment will need to be carried out by a person who is competent and understands all of the hazards and risks involved.
  2. Contact the local water supplier and the Environment Agency and inform them of what you intend to do. You may need their explicit permission before going ahead. Also, they will require you to remove all of the chlorine from the water prior to discharging and may also require you to discharge the water at a slower rate than you were originally intending.
  3. Before releasing any water, turn off the air and water heating system and let the temperature come down to as close to the ambient temperature as possible.
  4. Neutralise all of the chlorine in the water using sodium thiosulphate. Every 1 gram of free chlorine will need 5 grams of sodium thiosulphate to neutralise it. For example, if your pool volume is 450 cubic metres and your free chlorine reading is 2.0 mg/l, then there is 900 grams of free chlorine. Times this by 5 (4500g) and you have the amount of sodium thiosulphate you will need to add.
  5. Start discharging the water. This needs to be done slowly, at a rate of no more than 750mm per 24 hour period. So for a pool that’s 2 metres deep, it’s going to take the best part of 3 days to empty it.

Procedure for re-filling

  1. Before refilling, try to get the pool tiles to as close as possible to the incoming water temperature. This will obviously be more difficult to achieve in the winter months, so have a think about when would be the best time to schedule this work.
  2. Heat the water slowly at a rate of no more than 0.25 degrees Celsius per hour. So if the water is, say, 5 degrees Celsius, you may be looking at a four-day period in order to get it up to bathing temperature.

If a pool is emptied, then the bottom and sides should be scrubbed thoroughly with 10 mg/l chlorinated water before refilling. It should be flushed thoroughly to drain before refilling. Check the integrity of the structure while the pool is empty.