Why Does a Pool Lose Water After It Has Been Closed for the Season?

A closed pool can lose water because of a leak, a damaged cover, evaporation before freezing, or water being displaced by winter conditions. A modest change in water levels of your backyard swimming pool does not always indicate a serious problem, but a continuing drop should be investigated before the water falls below the level needed to support the liner or protect the pool structure. Along with sourcing Toronto pool supplies, owners should check the water level periodically throughout the off-season rather than waiting until spring to uncover a potential leak.

First, Determine Whether Water Is Leaving the Pool

Rain, snow, ice, and the type of winter cover can make the pool's water level difficult to judge. A solid cover may collect precipitation on top, while a mesh safety cover allows rain and melted snow to enter the pool. Water on top of a solid cover can also pull the cover downward and make the pool appear lower than it is.

Before assuming there is a leak, compare the current water level with the level recorded immediately after closing. Take a photograph at closing that clearly shows the water in relation to the skimmer, returns, steps, or liner pattern. This gives you a consistent reference point for winter checks.

Do not walk onto the cover or attempt to look beneath it in unsafe or icy conditions. Examine the pool from the surrounding deck and follow the cover manufacturer's instructions.

A Leak May Have Continued After Closing

Closing a pool does not stop an existing leak. Water can continue escaping through a damaged liner, light niche, fitting, gasket, return, skimmer, or underground line.

The level at which the water stops dropping can provide a clue. If it stabilizes near a return fitting, light, or another penetration, the leak may be associated with that area. This observation does not confirm the source, but it can help a technician decide where to begin testing.

A leak is more likely when:

• The water drops steadily during dry or consistently frozen weather
• The level falls well below its closing position
• Damp or unusually soft ground appears near the pool
• The cover loses support as the water drops
• The pool had unexplained water loss before closing
• The liner pulls, shifts, or develops visible wrinkles

Our guide to identifying a swimming pool leak explains additional warning signs owners may notice during the operating season.

The Cover Can Change How Water Moves

A torn, loose, or poorly fitted winter cover may allow debris into the pool and place uneven pressure on the water below. Water bags can also leak, roll, or shift, allowing a solid cover to move out of position.

Inspect accessible anchors, straps, water bags, and cover edges from the deck. Our online shop includes winterizing supplies, including water bags, plugs, and seasonal accessories for properly equipped pool closings.

Removing accumulated water from a solid cover may be necessary, but owners should use equipment intended for that purpose and avoid draining so aggressively that the cover is pulled out of position.

Could It Just Be Evaporation?

Some water can be lost to evaporation before the pool freezes, especially during dry, windy weather when the water remains exposed. However, evaporation should not cause a large, continuous reduction after the surface is frozen and the pool is securely covered.

Water may also leave the pool during the closing process if plumbing is drained, equipment is disconnected, or the level is intentionally lowered. That is why recording the final water level after all closing work has been completed is important.

Why a Low Water Level Should Not Be Ignored

Pool water helps support the liner and counteracts pressure from surrounding soil and groundwater. Allowing the level to fall too far can contribute to liner movement, cover damage, or stress on the pool structure. The exact risk depends on the pool type, cover system, site conditions, and how far the water has dropped.

Do not automatically refill a closed pool without determining why the level fell. Adding water can temporarily hide an active leak, and exterior hoses may be unavailable or unsafe during freezing conditions.

What Should You Check Safely?

From outside the covered pool, homeowners can:

• Compare the level with a closing-day photograph
• Check for visible tears or displaced cover sections
• Examine accessible straps, anchors, and water bags
• Look for wet ground or unusual settling
• Record whether the water continues dropping
• Note the approximate level where the loss stops

Toronto pool supplies such as winter plugs, water-testing products, cover accessories, and maintenance tools can support proper seasonal care, but they cannot repair an unidentified leak.

Protect Your Swimming Pool with Your Local Pool Experts

If the water continues falling, the cover loses support, or the liner begins moving, contact Seaway Pools & Hot Tubs. We can assess whether the change is consistent with the closing setup or whether the pool should be inspected for a leak before additional damage develops.