Draining an underground pool is a significant maintenance task that requires careful planning and execution. Whether you are preparing for the off-season, conducting repairs, or addressing a water quality issue, the process must be handled with precision. Unlike above-ground models, an underground pool presents unique challenges related to hydrostatic pressure and water disposal regulations. This guide provides a thorough, step-by-step approach to ensure the job is done safely and effectively.
Understanding the Risks and Preparing for the Task
Before turning on the first valve, it is critical to understand the inherent risks associated with draining an underground pool. The primary concern is hydrostatic pressure, the force exerted by the groundwater surrounding the pool shell. When the pool is full, this pressure counteracts the weight of the structure. Removing the water can cause the pool to float or "pop" out of the ground, leading to catastrophic structural damage. Furthermore, many municipalities have strict regulations regarding where the water can be discharged, as large volumes can overwhelm storm drains or harm local ecosystems.
Assess the Groundwater Level
In regions with a high water table, the danger of popping is exceptionally high. You must determine the current groundwater level in your area. This can usually be done by checking with local municipal water departments or well drillers. If the water table is high, you may need to install a temporary sump pump inside the pool to keep the water level below the floor during the draining process. This equalizes the pressure and keeps the pool shell securely in place.
Choosing Your Drainage Method
Selecting the right equipment is the next crucial step. While a standard submersible pump is common, you have options depending on your pool's size and local rules. The method you choose will dictate the speed and safety of the operation. Always remember never to drain the pool completely unless the groundwater is below the pool floor, and never drain on a day with heavy rainfall or flooding.
- Submersible Utility Pump: Ideal for medium-sized pools, these pumps are placed directly into the pool water and offer a good balance of power and portability.
- Trash Pump: Used for larger pools or situations where debris is present, these pumps can handle solids and move water quickly.
- Sump Pump: Often used to manage groundwater, a high-capacity sump pump can be used to drain the pool if the discharge hose is long enough.
The Step-by-Step Draining Procedure
Once you have assessed the risks and gathered your equipment, you can begin the physical draining process. Professional contractors often use a two-stage approach for large pools, but for routine draining, a single pump usually suffices. The goal is to control the flow rather than simply gushing water out, which helps maintain pressure balance.
Setting Up the Discharge Hose
Water disposal is often the most overlooked part of the process. You cannot simply drain the water onto the street or a neighbor's lawn, as this can cause erosion, landscaping damage, and potential code violations. Aim to discharge the water at least 10 feet away from the foundation of your home. Ideally, direct the hose toward a permeable area, a dry well, or a storm drain, ensuring you have the necessary permission to do so.
- Place the pump deep into the deepest part of the pool, submerged under the water level.
- Run the discharge hose to your chosen location, securing it to prevent kinking.
- If possible, slightly open the main drain drain plug to allow air to enter the system, which speeds up the flow.
Monitoring the Water Level
During the draining process, you must never leave the pump unattended. As the water level drops, you must physically check the floor and walls of the pool at regular intervals. The moment the water level reaches the bottom, you must stop the pump immediately, even if the pool looks empty. Continuing to run the pump at this stage will only suck in sand or damage the pool's plaster or liner.
The Equalization Check
When the pool is nearly empty, turn off the pump and wait for the water to settle. Use a ruler or measuring tape to check the depth of the water remaining in the corners. Then, carefully feel the floor of the pool. If the floor is firm and does not lift slightly when pressed, the groundwater pressure is likely balanced. If the floor feels spongy or lifts, you must stop immediately and contact a structural professional before proceeding further.
Final Steps and Post-Draining Maintenance
With the water removed, the real work begins. An empty pool is vulnerable to debris, animals, and structural shifts. You must protect the empty shell until you are ready to refill it. This phase is just as important as the draining itself to ensure the pool remains in perfect condition while inactive.
- Clean the Shell: Use a stiff brush to remove any remaining algae or scale. Rinse thoroughly to prevent mineral deposits from bonding to the surface.
- Inspect for Damage: Look for cracks, tears in the liner, or any signs of settling. Now that the water pressure is gone, small issues become much easier to spot.
- Keep it Covered: Secure a heavy-duty pool cover or at minimum a breathable pool tarp. This prevents rainwater from accumulating in the shell and provides a barrier against leaves and animals.
Draining an underground pool is a manageable task when approached with the right knowledge. By respecting the forces of hydrostatic pressure and planning your discharge strategy, you can complete the job without incident. Taking the time to follow these steps ensures your pool remains a valuable asset to your property for years to come.
