Ponding water often doesn’t create many immediate problems, other than standing water on your roof. It creates many long-term problems, however. As mentioned above, it can cause algae growth on your roof, which can hurt your roof membrane. Algae often damages the seams of single-ply roof membranes. Ponding water can also freeze in colder temperatures. Freezing causes the water to expand and exert extra pressure on the roof membrane. Along with those two effects, pools of standing water can magnify sunlight as it hits your roof, which increases the damage UV rays can do to its membrane. All these problems age your roof membrane prematurely and shorten its overall lifespan.