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Winterizing Outdoor Swimming Pools

by Manfred F. Judematz, P.E.

In response to a number of inquiries from municipal and private swimming pool owners and operators, I have prepared the following suggested procedures for winterizing outdoor swimming pools. The procedures are intended to minimize possible damage caused by freezing temperatures. The discussion presented is not tailored to any particular type of pool or equipment manufacturer, and is generally applicable to all pools.


Swimming Pools may or may not be drained completely, if not drained completely, the water level should be lowered to approximately 12" below the pool lights. Water left in the pool will tend to give protection to the joint sealants.

The following steps are recommended: Open drain valve at Filter Tank and start draining pool through Filter or if the pool has a main drain bypass, drain through it. When water level drops below the high point in the filtered water supply line, flow from pool through Filter will cease and the supply line from Filter to Inlet Header around pool should be empty. Leave Filter Tank drain open until Tank and piping are completely drained. Make sure there is no water left in the supply line between pump and the high point at supply line by partially removing valve on supply line at Filter or in Filter Pit. After this is completed, open main drain valve on pool drain line if water in pool has not reached the desired level and continue to drain pool until it reaches the suggested level below lights, or until it drains completely. Some pools may not drain completely by gravity and will need to be pumped out.

Logs or barrels to break the water surface are not recommended unless they can be positively held in place by anchoring to the pool bottom.

If some water is left in the pool, add recommended winter dosage of algaecide to pool water every other week until water freezes and continue this treatment in spring until pool is put back in operation.

If your pool has a Hydrostatic pressure relief valve at the bottom of pool, leave it closed when water is left in pool.

Drain wading pool completely and leave all valves on drain and supply line open.

Remove skimmer basket at wading pool and place old clothes or towels in skimmer housing, then replace cover and store basket.


Remove diving boards from stands and store in a dry sheltered place. Do not store heavy items on the boards, and do not store them flat unless continuously supported.

All removable items such as ladders, diving stands, guard chairs, and hand rails, and other accessory equipment (vacuum cleaner, deck drain, benches, umbrellas) should be stored inside the bath house or filter room. Store all hoses inside.

Check deck hydrants and make sure they are open at the hydrant and at their supply source.


The main drain valve on the pool drain line should be closed tightly after lowering of water level, or left completely open if pool is drained. If there is no valve on main return line to filter (outside of filter pit) the pool water has to be lowered until it reaches the flow elevations of this pipe at filter tank. This will drain the exposed portion or the main return in filter room. If this is not desired, a thermostatically controlled heater should be installed in the filter pit to prevent the line from freezing.

Make sure the skimmer, main pool and wading pool return lines are drained within Filter Room and leave all valves open. Open all valves to drain filter cell and pre-filter chamber.

Be sure to drain the manifold in the filter tank. It may be necessary to loosen the bolts on the flange union connecting the pump and filter to allow this to drain, depending upon the design of the pump installed.

Clean Filter elements and filter tank and leave drain valve at Tank open. Be sure all valves from filter to storm sewer line or outfall line are in open position. Wash the elements clean with a hose and wash bottom of the filter clean.

On Filters having removable elements, remove the elements for inspection to be sure they are absolutely clean.

Illinois Parks and Recreation 10 July/August, 1977

Store filter elements in an upright position in a dry place. It is recommended that they be placed in cardboard cartons.

Clean container of soda ash feeding unit and drain hose to filtered water supply line. Disconnect Feeder pump and store in a dry place. Leave all valves open.

It is preferred that all chemicals in Filter room be stored above the floor (use 2 x 4's spaced 4 inches on center) and leave space along outside walls.

Disconnect chlorine cylinder and return same with any remaining unused cylinders to Supplier. Drain potable water line to chlorinator, and all water from chlorinator. Leave drain plugs out.

Empty diatomaceous earth Feeder and wash thoroughly with water. Drain purge water line or vibrator type Feeders, leave drains open.

Open valve on make-up line to drain pipe, leave valve open.

Open drain valve or remove bottom plug on Filter pump for complete drainage of pump housing. Be certain there is no water left in the pump. Reference is made to pump operators manual usually furnished with equipment at the time of installation.

At the bottom of the Mercury Manometer is a small drain opening. Hold a clean bottle under this opening and drain the mercury and water from the Manometer. Remove excess water from the mercury, stopper, and store the mercury in a safe place. Inspect all lines to make sure they are completely drained.


Do not have power supply shut off, but turn all main disconnect switches to "off." Usually it costs less to pay the small monthly charge during the winter than to pay the service charge for reconnecting the power in spring. In addition, there is power available when needed for maintenance work.

Turn off all light and power switches and shut off and unplug all electrical appliances.

Drain hot and cold water piping completely at low points in line by using proper drain valves. Open shower valves to allow water to drain, if possible remove shower head and valve and leave pipe open. Leave all valves and hose bibbs open. Have Utility Company shut-off main water supply and remove or drain water meter. Drain mixing valve. Leave all valves and drains open, leave all drain plugs out.

Drain and clean water heaters and storage tank as recommended by the manufacturer's manuals. Leave drain valves open.

Have Utility Company turn-off main gas supply as necessary and turn off all gas stop cocks and pilot light at water heater.

Place anti-freeze in all floor and shower drain traps.

Drain Flush Tanks of toilets and urinals and place anti-freeze in traps or lower water level and add suitable quantity of antifreeze. Keep seat cover closed. Cover urinals and toilets with polyethylene sheet to keep out moisture which could displace anti-freeze in trap.

Drain traps of lavatories and drinking fountain by removing plug at gooseneck and leave open.

Open roofs can be closed with 3/8 inch (minimum) plywood sheets fastened with carriage bolts and wing nuts or with wire tied to joists. Cover plywood sheets with polyethylene and staple to plywood. This is not a water-tight protection, but will keep out most of the moisture, snow, and other debris.

All other unprotected openings in outside walls (entrances, check windows, etc.) should be closed in a similar manner to the method suggested for roof openings, but polyethylene sheets may be omitted.

Lock all doors and gates securely and be sure windows are closed and locked.

Wrap polyethylene sheeting around drinking fountain and hold wrapping in place with strings or staples. Leave drain plug out.

It is recommended that removable bicycle racks be placed inside the pool enclosure.

The electric clock should be disconnected and stored inside the office. All loose deck items, signs etc. should be suitable stored.

Lubricate all motors and change the oil in any speed reducers, gasoline engine-driven vacuum cleaner pumps, etc. in accordance with manufacturer's instructions. Drain any pumps that are stored.

In general leave all valves and plugs open, cover exterior motors and equipment. Clean up all debris, left over towels, shoes, etc.

(Editor's note: Mr. Judernatz is vice president of Gollehon, Schemmer, and Associates, Inc.)

Illinois Parks and Recreation 11 July/August, 1977

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