From: veritasium
Shade balls are small, black, partially water-filled spheres used to cover open water reservoirs, particularly in places like Los Angeles [00:00:06]. While often misunderstood as primarily for evaporation reduction [00:10:00], their main purpose is to address specific water quality issues and provide various other benefits [00:17:00]. The LA Reservoir alone uses 96 million shade balls [00:32:00].
Primary Benefit: Preventing Bromate Formation
The primary reason for deploying shade balls in the Los Angeles Reservoir was to prevent the formation of Bromate [03:05:00].
- The Problem: Bromide is a naturally occurring, harmless substance found in water, especially from sources like the California Aqueduct [03:08:00]. While harmless on its own [03:21:00], when Bromide combines with Chlorine (a necessary disinfectant) [03:34:00] under bright sunlight [04:18:00], it forms Bromate, which is carcinogenic [03:30:00]. This discovery was made when a beverage company customer found high Bromate levels in water from the reservoir [03:54:00].
- The Solution: With Bromide and Chlorine being unavoidable, the only choice was to remove sunlight [03:39:00]. After considering various options like floating tarps or pipe debris [04:42:00], shade balls (originally called “bird balls”) were identified as an effective solution [05:24:00].
- Testing: Initial tests using kiddie pools showed that shade balls immediately solved the Bromate problem [06:30:00].
- Color: Shade balls are black to block all light from reaching the water [06:44:00]. This color is achieved using “carbon black” pigment, which ensures the plastic’s stability and longevity (at least 10 years) when exposed to sunlight [07:10:00]. Other colors tested were unstable [07:17:00].
Additional Benefits
Beyond Bromate prevention, shade balls offer several other advantages:
- Algae Control: Blocking sunlight eliminates algae growth in the water [08:41:00]. This significantly reduces the need for Chlorine, which was previously used extensively to control algae [08:46:00].
- Evaporation Reduction: Despite their black color, shade balls reduce evaporation by 80 to 90% [09:58:00]. This occurs because:
- They reduce the exposed surface area of the water [09:15:00].
- They prevent dry air from continually replacing moist air directly above the water [09:20:00].
- The balls are partially filled with air, which acts as a thermal insulator [09:35:00], preventing heat from the sun-heated top of the ball from transferring to the water below [09:38:00]. In fact, the water under the shade balls is actually cooler than an uncovered reservoir [09:48:00].
- Bird Deterrent: Originally known as “bird balls,” they effectively deter waterfowl from landing on the reservoir [05:36:00]. This is beneficial for preventing bird droppings from impacting water quality [06:17:00] and also prevents birds from getting poisoned by contaminated ponds or interfering with aircraft near airports [05:39:00].
Costs and Savings
Shade balls are relatively inexpensive.
- Purchase Cost: They cost approximately 33-34 cents per ball, or about three for one dollar [10:07:00].
- Material and Safety: They are made from high-density polyethylene, the same food-grade plastic used for milk jugs [06:59:00]. The material is safe for drinking water contact [06:50:00] and inert [07:40:00].
- Long-term Value: Over their lifespan, the savings from reduced chlorination chemicals and evaporation are expected to cover at least half of the balls’ cost [10:21:00]. Additionally, they have a salvage value as they are recyclable material [10:13:00]. The water quality benefit is considered immeasurable [10:33:00].
Design and Handling
- Weighting: Shade balls are partially filled with water to prevent them from being blown away by high winds [01:19:00]. The uneven water distribution makes them wobble if they do roll [01:36:00].
- Movement: Moving through shade balls (e.g., by boat) is very difficult because they form dense, “close packed crystal-like structures” [01:12:00], making it feel like driving through peanut butter [08:12:00]. Despite breezes, they remain very stable on the water’s surface [07:56:00].
- Shape: The spherical shape is crucial because it prevents them from stacking up or perching on the reservoir banks as water levels fluctuate [11:05:00], ensuring they spread out to cover the water effectively [11:18:00]. Other shapes like hexagons were considered but were not suitable [10:58:00].