Should I drain my Ottawa pool partially or fully before closing it for winter?

You should drain your Ottawa pool partially — lowering the water level 10 to 15 centimetres below the skimmer mouth — rather than draining it fully, which can cause severe structural damage to your pool in Ottawa's frost-prone clay soils. A fully drained inground pool in Ottawa risks hydrostatic uplift, where groundwater pressure beneath the pool shell literally pushes the empty pool upward out of the ground, cracking the shell and destroying the structure.

The reason partial draining is critical relates directly to Ottawa's geological and climatic conditions. The Ottawa region sits on Leda clay (also called Champlain Sea clay), a notoriously unstable soil type that retains significant moisture and exerts substantial hydrostatic pressure when saturated. During fall rains and spring snowmelt, the water table in many Ottawa neighbourhoods rises dramatically. A full pool acts as a counterweight against this upward pressure. Remove that weight by draining completely, and the buoyant force of groundwater can lift a fibreglass pool entirely out of the ground or crack a concrete pool shell — damage that costs $10,000 to $50,000 or more to repair, if repair is even possible.

The correct water level for winterizing an Ottawa pool depends on your pool type and plumbing configuration. For pools with standard wall-mounted skimmers, lower the water to 10 to 15 centimetres below the bottom of the skimmer opening. This puts the water level below all plumbing penetrations in the pool wall, allowing your technician to blow out and antifreeze the lines without water flowing back into them. For pools with in-floor cleaning systems or vanishing-edge designs, the technician may set a different level based on the specific plumbing layout — always follow their guidance rather than using a generic rule.

Some Ottawa pool owners ask about draining vinyl liner pools, and the answer is an emphatic no. A vinyl liner that dries out contracts, becomes brittle, and develops creases and wrinkles that never fully smooth out when the pool is refilled. Worse, removing the water weight from a vinyl liner pool allows the sand or vermiculite base beneath the liner to shift, heave, or erode, creating an uneven floor that shortens the liner's lifespan and creates uncomfortable or even unsafe footing. The cost of a new liner installation in Ottawa runs $3,500 to $7,000 for a standard residential pool — damage that is entirely avoidable by maintaining proper water levels.

Concrete and gunite pools can tolerate more water removal than fibreglass or vinyl, but full drainage is still dangerous in Ottawa. Even the structural rigidity of a reinforced concrete pool shell is not designed to resist the hydrostatic pressure exerted by Ottawa's clay soils and seasonal water table fluctuations. If you must drain a concrete pool for repairs, it should be done during the driest period (typically July to August), with hydrostatic relief plugs opened at the pool floor to equalize pressure, and the pool should be refilled as quickly as possible — ideally within 48 to 72 hours.

The water remaining in your pool over winter serves several important functions beyond structural ballast. It protects the pool finish from freeze-thaw damage at the waterline, supports the winter cover by preventing excessive sag, and provides thermal mass that moderates temperature swings in the pool structure. Pool professionals in Ottawa often add a winterizing chemical treatment to this remaining water — typically $40 to $80 worth of algaecide, stain preventive, and an oxidizer — that keeps the water relatively clean through the 5 to 6 months of cover-on dormancy.

One common mistake Ottawa homeowners make is failing to account for rainfall and snowmelt during winter. After you lower the water level in October, autumn rains and eventual snowmelt through the cover can raise it back to or above the skimmer level by spring. This is normal and not a cause for concern — the water has nowhere to go that would cause damage. However, if your pool has a mesh winter cover, which allows precipitation to filter through, the water level may rise significantly over winter. Your spring opening technician will address the water level as part of the standard opening procedure.

If your pool technician ever suggests fully draining your pool for winterization, ask them to explain exactly why. The only legitimate reasons to fully drain an Ottawa pool are major structural repairs, liner replacement, or replastering — all of which should be done during summer, not as part of closing. A pool closing service that routinely fully drains pools either does not understand Ottawa's soil conditions or is cutting corners on the winterization process.

Neighbourhood-specific drainage considerations across Ottawa add another layer to this decision. Homes in Riverside South, parts of Barrhaven, and the Rideau River corridor experience some of the highest water tables in the city, making full drainage especially dangerous in these areas. Properties in Kanata and Stittsville built on the older rock formations of the Canadian Shield may have lower water tables, but the unpredictable nature of Ottawa's spring snowmelt means even these areas can experience temporary water table spikes. Orleans and Cumberland, situated in the Ottawa River floodplain, carry additional groundwater risks during spring freshet. Regardless of your neighbourhood, the universal rule applies: never fully drain an inground pool in Ottawa without professional guidance and a clear structural reason.

Have questions about the right winterization approach for your Ottawa pool? Ottawa Pool Installation can connect you with experienced local professionals who understand the unique challenges of closing pools in Ottawa's clay soil environment.