The concern over pool water affecting a lawn is common for homeowners managing splashing, routine backwashing, or full draining near turfgrass. The effect of this water on grass is complex and depends heavily on the concentration of chemicals and the overall volume of water involved. Small, localized exposure may cause minimal impact, but large volumes of chemically concentrated water can severely damage or kill a lawn. Understanding these factors is necessary to protect the surrounding landscape.
Chemical Factors in Pool Water That Harm Grass
Chlorine and bromine, the primary sanitizers in many pools, are strong oxidizing agents that can cause direct phytotoxicity, or chemical burn, to grass blades. High concentrations of these chemicals rapidly denature plant tissues and inhibit the function of chloroplasts responsible for photosynthesis. This chemical disruption manifests visibly as yellowing, browning, or dead patches.
Salt, specifically sodium chloride used in saltwater pools, poses a different, longer-term threat to grass health. Sodium ions in the soil create an osmotic imbalance, actively drawing moisture out of the grass roots, leading to dehydration known as “physiological drought.” Elevated sodium levels also compete with essential nutrients like calcium and magnesium for binding sites on soil particles. This inhibits nutrient uptake and leads to deficiencies that cause discoloration and stunted growth.
The pH level of the pool water, typically maintained between 7.2 and 7.8, can stress the lawn if highly unbalanced. Grass thrives in a near-neutral soil pH, ideally between 6.0 and 7.0. Water that is excessively alkaline (high pH) or acidic (low pH) alters the soil chemistry. This makes it difficult for the grass to absorb necessary nutrients like iron, phosphorus, and potassium, resulting in weak, unhealthy growth.
Damage Severity Based on Water Volume and Type
The extent of the damage is directly related to the quantity of water and the pool type. Minor exposures, such as splashing or small amounts of backwash, rarely cause lasting damage to a well-maintained lawn. The chemicals in these small volumes are diluted by existing soil moisture and ambient conditions, allowing them to dissipate quickly with only localized, temporary yellowing of the grass blades.
Major exposures, such as draining a pool or a significant leak, present a severe risk because the large volume saturates the soil with chemicals. Water freshly treated with chlorine is more toxic than water that has sat for several days without chemical addition. This high concentration of chlorine or bromine can kill the grass and disrupt the soil’s microbial balance, requiring extensive recovery efforts.
Saltwater pools, while often having lower concentrations of sanitizers, pose a greater long-term threat during a full drain due to the non-dissipating nature of salt in the soil. Unlike chlorine, which volatilizes into the atmosphere, sodium chloride remains in the root zone, increasing soil salinity. This salt buildup can lead to soil compaction, especially in clay-heavy soils, which further restricts the grass’s ability to absorb water and nutrients.
Strategies for Prevention and Lawn Recovery
Preventing pool water damage involves proactive steps focused on dilution and chemical neutralization. Before draining a pool or performing a major backwash, water the lawn heavily with fresh, clean water to pre-saturate the soil. This foundational layer of moisture helps immediately dilute the concentration of pool chemicals that reach the root zone.
For chlorinated pools, allow the water to sit for at least 24 to 48 hours without adding new chemicals before draining. This time allows the free chlorine to naturally dissipate or volatilize into the air, reducing the chemical’s toxicity to the grass. When draining, redirect the water away from sensitive turf areas using a temporary hose or a drainage system leading to a sanitary sewer or storm drain.
If damage occurs, the first recovery step is to thoroughly wash the affected area with fresh water to leach the chemicals past the root zone. For salt-affected areas, apply a soil amendment like gypsum (calcium sulfate). The calcium ions in the gypsum displace the sodium ions attached to the soil particles, allowing the harmful sodium to be flushed out with subsequent deep watering. Severely damaged or dead turf patches may need to be removed and replaced by reseeding or sodding to fully restore the lawn.