Of all the causes of pool leaks, nothing is quite as insidious as a leak in the main drain. Located at the deepest part of the pool, the main drain functions as a key component of the circulation and filtration system by pulling water and debris to the pump. Along with the skimmers, the main drain is one of the pool’s water outlets that draws water to be filtered before being returned to the pool. The main drain also provides a way to drain the pool for repair if necessary, as well as helps to prevent water stagnation and maintain even water chemistry and temperature.
By the way, please note that a pool should never be drained by anyone other than a licensed pool contractor! Our blog post – “Why You Should Never Drain Your Pool Yourself” – covers this important topic in detail.
What is a Pool Main Drain Leak?
Simply stated, a pool main drain leak is when the piping or fitting at the bottom of the pool fails, causing water to escape the pool and drain into the ground. This type of leak can be hard to detect because the plumbing is usually buried under concrete or the pool bottom, but it can result in significant water loss, potentially damaging the pool structure. Our blog post – “Does Your Inground Pool Have a Pipe Leak?” – covers this type of leak (and others) in detail.
Possible Causes of a Pool Main Drain Leak
This type of leak can occur for many different reasons, all of which are not readily detected by the homeowner. The following are the most common:
Cracked or loose drain cover – A damaged or improperly installed drain cover can allow water to escape.
Cracked plumbing lines – The PVC pipes connecting the main drain to the pump can develop cracks from age, ground movement, or improper installation.
Faulty hydrostatic relief valve – This valve allows groundwater to enter the pool to relieve pressure. Debris can get stuck, causing the valve to remain open and leak water.
Shifting soil or ground movement – Settling or movement of the ground around the pool can stress and crack the main drain line or fittings.
Corrosion and chemical damage – Over time, harsh pool chemicals can corrode and degrade pipes and fittings, leading to leaks.
Loose fittings or deteriorated seals – Fittings and valves in the drain line can deteriorate or become loose, causing them to leak.
Age of the pool system – Older pools may experience leaks due to the general wear and tear on the plumbing system over time.
Damage from pool maintenance equipment – Sometimes, the very tools used to maintain your pool can cause damage. For example, using heavy-duty cleaning equipment near the main drain could accidentally damage it.
Damage That a Main Drain Leak Can Cause to Your Pool and Property
As the good people at Leak Rescue point out, a leak in the main drain can lead to more than just water loss. Because the main drain is connected to the deepest part of the pool, a leak here can go undetected for longer, making the damage worse. Over time, leaking water can:
- Undermine the pool shell, causing cracks or shifting.
- Cause structural damage to the concrete deck – such as cracks, sinking and lifting – due to shifting.
- Damage the pool pump and surrounding equipment.
- Damage the pool bottom and surrounding soil.
- Cause erosion around the pool plumbing lines – in Florida, this could create conditions for a sinkhole.
- Lead to costly repairs if ignored.
- Lead to significantly higher water bills, as constant water loss requires frequent refilling.
Signs That Your Pool May Have a Main Drain Leak
Because a main drain leak is unlikely to be observed directly, being alert for signs that indicate this type of leak is essential for early detection and timely repair. Look for the following:
- A water level that drops more than ¼ to ½ inch per day (beyond normal evaporation).
- Soggy spots in the landscaping or around the pool area.
- A pool that requires frequent, weekly refilling.
- Cracks or uneven areas in the pool deck.
- Cracks near the main drain cover: Visible damage or loose fittings at the bottom of your pool can be a red flag.
- Cracks in the pool wall or bottom.
- An increase in your water bill.
- Air bubbles coming from the main drain – they indicate that air is being sucked into the system through a crack or hole.
- Unusual noises from the drain – Gurgling or hissing noises near the main drain are not normal and should be investigated, as they may signal a leak.
- Dirt or debris around the main drain – If there’s an unusual amount of dirt or debris around the main drain, it could mean that soil is being pulled into the pool through a leak.
- Increase in pool chemical use – A sudden need for more chemicals to maintain the pool’s balance can be a sign that water is escaping and being replaced at a rate higher than usual.
The Take-Home Message
A main drain leak in your pool can have damaging consequences if it goes undetected. If you’re the type of pool owner who likes to troubleshoot, be aware that DIY detection methods such as the “bucket test” for water evaporation – which our website describes in step-by-step detail – and the dye test have their limitations for this type of leak. For example, the bucket test can indicate that your pool has a leak, but not its location.
The integrity of your pool – and your home’s foundation – are too important to wait. Call Certified Leak Detection for quick, accurate detection of even the most hard-to-locate pool leak. We use technology and techniques we’ve developed over 20 years in business – such as non-invasive ultrasonic detection technology. In addition to detection of pool leaks, we provide industry-leading leak detection for spas, hot tubs and fountains, as well as slabs and foundations. Serving areas throughout Central Florida – including Orlando, Longwood, Lake Mary, Sanford, Kissimmee, Clermont and Winter Springs – we are ready to answer your call. Contact us for fast, reliable service!