tap water

Tap Water: Friend or Foe to the Reef Keeper?

Tap water: Friend or Foe to the Reef Keeper?

For many aquarists tap water is just “water.” You add it to the tank and never give it another thought. But for the reef aquarist tap water is the lifeblood of the aquarium. The purity of the water we use to mix our saltwater or just top off our tanks is critical for keeping a healthy reef.

 Where does tap water come from?

There are many sources of tap water. The most basic source is a private well. A pump draws underground water from the well and delivers it to your faucet. Other water sources include lakes, rivers, deep wells and man-made reservoirs. Rain often keeps these water sources topped off. Towns and cities rely on centralized water treatment plants to process and distribute water to homes and business. Water may be pumped from great distances to supply a city with water. Some towns have several wells scattered throughout the area. Your next-door neighbor’s water source could be different than yours!


tap water

By Anita Martinz from Klagenfurt, Austria

What is in my tap water?

With so many sources, the chemical make-up of tap water can vary even within the same town. The natural geology has a major influence on the water chemistry. If the rocks surrounding the water source are high in calcium and magnesium carbonate, they will dissolve into the water and create “hard” water.  Hard water tends to have a high pH and leaves white deposits in the shower and on fixtures. At the other extreme, some water supplies are naturally “soft,” low in minerals. Naturally soft water can be corrosive, causing copper to leach from the pipes. Most tap water supplies are somewhere in between these extremes. Your tap water will contain many natural elements such as sodium, potassium, chloride and sulfate. These are harmless and actually give drinking water a pleasant flavor.  The United States Environmental Protection Agency sets drinking water standards to ensure drinking water is safe for consumption. These rules must be followed by every local water treatment facility. Disinfectants, like chlorine and chloramine, are added to kill bacteria, viruses and protozoa. To prevent corrosion, phosphate-containing corrosion inhibitors are often added to protect the pipes. Your tap water may contain nitrate. Nitrate leaches into the water supply from fertilizers, animal farms, septic systems and natural sources. Carcinogenic arsenic leaches into groundwater naturally from rocks. Non-toxic silicate is in all water supplies, and can stimulate diatom algae in aquariums.

Is tap water safe for my reef?

Browse through any aquatic supply catalog and you’ll find several types of tap water filters designed to remove the “bad stuff” and keep your tank safe. You may be tempted to think that all tap water sources are harmful to the aquarium. The truth is most water supplies are acceptable for reef use. But some are not. So before buying an expensive water filtration system, take a look at your tap water quality. Your water treatment facility publishes an annual test report. It will show you the levels of contaminants like nitrate and heavy metals. You can also test for copper, nitrate and phosphate yourself or have your local shop do it for you. The better reef shops will have these tests available for diagnosing water quality issues. Then you will know if you really need a tap water filter.

Common sense solutions

If your reef is looking good, there is no need to buy an expensive tap water filtration system. If, however, you have chronic problems that are caused by something in your tap water – you may need a RO/DI unit to purify your water and remove the source of the contamination.

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