It’s amazing what you learn when you’re out in the field. I can’t tell you how many times we ask industry members, “Did you check the fill water?” -- and the answer is “no” or “I forgot.” The National Plasterers Council has stressed for decades the need to test the fill water on any pool that has been drained for remodeling, renovation or a simple repair prior to filling.

A variety of problems may arise from three fill water factors: (1) tap or fill water that is potentially aggressive due to low pH, low calcium hardness or low carbonate/total alkalinity (2) tap or fill water that has high pH, high calcium hardness or high total alkalinity contents or (3) some fill waters may have elevated levels of dissolved metals in them, the  most common being copper and iron, and sometimes manganese.

Low levels of calcium hardness, total alkalinity and low pH can lead to etching of surfaces,
dissolution of grouts, and damage to the pool equipment. These problems can be visible in the pool as surface discoloration issues, colored water, and deteriorated metals in pumps, heaters, valves and other metal components.

High calcium levels, high total alkalinity and high pH may lead to problems such as scaled pool surfaces, staining discoloration, cloudy water, and equipment issues such as plugged filters and heaters, along with poor circulation.

Dissolved metals in the tap water can lead to colored pool water and staining discoloration of
surfaces and grouts.

The best method to prevent problems from these three factors is to obtain good, commercially
available test kits and test the tap water pH, total alkalinity and calcium hardness. Specialty kits also are available to test for common metals. Anyone performing start-ups of new pools or newly remodeled pools should purchase test kits that are capable of testing the fill water for these factors. This includes plasterers, builders, remodelers and service companies.

Even those who do minor pool repairs where draining a pool is required should make it a standard procedure to test the tap water prior to filling.

It is strongly recommended to make testing of the fill or tap water mandatory at every start-up or refill, no matter what type of start-up procedure is implemented.