Fiberglass pools are popular backyard entertainment centers. In most cases, they are less expensive to install and maintain than traditional concrete swimming pools. They are less prone to cracking than concrete and will tolerate a greater pH range as well. In most instances, you can clean a fiberglass pool without the need for draining. In cases where emptying the pool is the only option, exercise extreme care.
Poorly anchored pools may float or buckle. Fiberglass pools are designed to be dimensionally stable when buried in the ground and filled with water. Pool manufacturers count on the weight of the water on the inside of the pool to counteract the weight of the earth and water on the sides and bottom of the excavated hole. Removing the water from the pool leaves only a thin (usually less than 1 inch thick) layer of fiberglass to hold the weight of the earth surrounding and supporting the pool. Removing the supporting weight from the pool's interior can result in bulges or cracks in the side of the pool. This is a particular danger in areas with loose sandy soil.
Groundwater is another element that may damage a drained pool. In areas with high water tables, or during periods of heavy rainfall, the weight of the water present in the soil surrounding the pool can deform the sides or bottom of the fiberglass shell. Water seeks its own level. A pool with an 8-foot depth in soil where the water table is at 6 feet will have a significant amount of pressure exerted across the entire bottom surface of the pool.
Pool water contains a considerable amount of chemicals. Drain pool water onto the ground or into a sewage or septic system only after careful consideration and/or consultation with local regulatory agencies. Significant amounts of chlorine can damage lawns and septic systems. Contact municipal authorities prior to filling storm drains or sewage lines with chemically treated water.
Installation contractors may be able to offer advice and assistance when there is no alternative to draining a pool. Interior structural bracing may be an option in areas with loose soil. In areas with high water tables, temporary wells or permanent standpipes may be options. Hiring insured, professional contractors to prevent unnecessary damage will cost less than replacing the pool.