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It is important to check the drain valves for correct operation prior to flight. Water ballast should drain from each wing tank at the same rate. Unequal draining leads to a wing-heavy condition that makes in-flight handling, as well as landings, more difficult. If the wing-heavy condition is extreme, it is possible the pilot will lose control of the glider. 

Ballast drains should also be checked to ensure that water ballast drains properly into the airstream, rather than leaking into the fuselage and pooling in the bottom of the fuselage. Water that is trapped in the fuselage may flow through or over bulkheads, causing dislocation of the CG of the glider. This CG dislocation can lead to loss of control of the glider. 

The flight manual provides guidance regarding the length of time it takes for the ballast tanks to drain completely. For modern gliders, it takes about 3 to 5 minutes to drain a full tank. When landing is imminent, dump ballast early enough to give the ballast drains sufficient time to empty the tanks. 

Use of water ballast when ambient temperatures are low can result in water freezing the drain valve. If the drain valve 

freezes, dumping ballast is difficult or impossible. If water in the wings is allowed to freeze, serious wing damage is likely to occur. Damage occurs because the volume of water expands during the freezing process. The resulting increased volume can deform ribs and other wing structures or cause glue bonds to delaminate. When weather or flight conditions are very cold, do not use water ballast unless antifreeze has been added to the water. Prior to using an antifreeze solution, consult the GFM to ensure that antifreeze compounds are approved for use in the glider. 

A glider carrying large amounts of water ballast has noticeably different handling characteristics than the same glider without water ballast. Water ballast: 

• Reduces the rate of acceleration of the glider at the beginning of the launch due to the increased glider weight. 

• Increases the length of ground roll prior to glider liftoff. 

• Increases stall speed. 

• Reduces aileron control during the takeoff roll, increasing the chance of uncontrolled wing drop and resultant ground loop. 

• Reduces rate of climb during climb-out. 

• Reduces aileron response during free flight. The addition of large amounts of water increases lateral stability substantially. This makes quick banking maneuvers difficult or impossible to perform. 

Water ballast is routinely dumped before landing to reduce the weight of the glider. Dumping ballast: 

• Decreases stall speed. 

• Decreases the optimum airspeed for the landing approach. 

• Shortens landing roll. 

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