With more than 30 years’ experience in the residential and commercial water treatment space, Mark Nelson is a Class 1 Drinking-Water Operator and a CBWA (Canadian Bottled Water Association) Certified Plant Operator. As founder and president of Nelson Water in Ottawa, Mark focuses on dealing with challenging water treatment system designs for problem water. He also heads the largest water bottling plant in the city of Ottawa with a delivery network throughout the Valley.
These days, there seems to be water quality issues reported in the media practically every day. While you may have heard about issues with iron, lead, or other well-known contaminants, you may not have thought about silica in your water supply. So, here we’ll delve into this water contaminant and whether you should feel concerned about the issue.
The Silica Basics
Silica is often known as SiO2 or silicon dioxide. This is a crystalline compound that is a common component in sand, minerals, and many rocks. It is formed when silicon and oxygen molecules merge with another mineral or metal. The levels of silica in nature can vary from 1 part per million to over 100 parts per million.
Generally speaking, there are two forms of silica that exist in water supplies. Reactive silica is any type of monomeric silica. In simple terms, this means any silica molecules that have reacted with other molecules. This can create ionized forms of silica or dissolved silicon dimers. So, reactive silica is a non-polymeric type of silica.
The other type of silica in water supplies is colloidal silica. This occurs when silica particles are suspended in the liquid. The silica is typically spherical particles that are non-porous and amorphous. Additionally, the surface of the silica particles that are in contact with the liquid is covered with siloxane bonds, creating a hydrophilic substance that can form hydrogen bonds.
Is Silica in Water a Problem?
Silica is often confused with water hardness as it can cause similar problems. You may notice scratching, spotting, or etching on your glassware or fixtures. It can also accumulate on surfaces to form scale. This scale acts in the same way as the hard water scale, accumulating inside water using appliances and fixtures to compromise performance and efficiency. It can interfere with water flow, interfering with water heaters and other systems that require a defined pressure range to operate correctly.
An easy way to determine if you have a hard water problem or silica water contamination is to apply vinegar to any scale accumulations. If you can remove the stain with vinegar, it was caused by water hardness. But, if the vinegar does not remove the stain, it was most likely caused by silica.
Fortunately, like hard water, silica does not pose a danger to health. Silica is not considered harmful if ingested in small quantities in drinking water. In fact, many foods such as onions, wheat, oats, root vegetables, and strawberries contain silica.
It is worth noting that if you have colloidal silica, you may find the water unpalatable. Many people find drinking water with floating bits of minerals in it unappealing. This may lead to drinking less water, putting you and your family at risk of dehydration. Additionally, the silica particles may react when you use the water to prepare tea or coffee, increasing its unpalatability.
So, while it may appear that the effects of silica in your water are purely aesthetic, there are some compelling reasons to address this water quality issue.
Methods to Remove Silica From Water Supplies
Since silica is such a common naturally occurring mineral, there are actually a number of methods that can be used to remove it from water supplies.
Lime Softening:
This process involves adding calcium hydroxide to the water. This creates a reaction where calcium carbonate and magnesium carbonate precipitate out. The calcium and magnesium hydroxides absorb the silica particles, removing them from the water supplies.
The most common application for this treatment method is commercial. It is used in large boiler feeds and large cooling towers. Since it requires a large capital investment and there are ongoing expenses for the necessary chemicals, it is not economically practical for residential applications.
Ion Exchange:
Ion exchange is a common method for removing hardness particles. So, it is logical that you may assume that ion exchange could be a viable method to remove silica. Silica molecules do have a negative charge, so you would need anion resin to remove them. Unfortunately, anion resin needs to be regenerated using caustic soda. This is a massive safety concern, particularly for residential water supplies, so ion exchange is not recommended for silica removal.
Ultrafiltration:
Ultra filtration or UF can be an effective treatment, but it will only remove colloidal silica. You will need to determine if the silica in your water supply is reactive or colloidal silica. You can accomplish this using a UF Pilot Stick. Connect this device to your garden hose and allow several gallons to run through. This will validate the presence of reactive or colloidal silica. If you find you have colloidal silica, you can then implement an ultrafiltration system.
Electrocoagulation:
This is a relatively new and emerging technology. It shows promise, but it is more applicable to industrial or municipal water treatment. Due to the infrastructure needed and treatment process, it is unlikely that this method will be appropriate for residential applications.
Reverse Osmosis:
RO or reverse osmosis systems feature a membrane. Water is forced through the membrane, and 99% of contaminants can become trapped. RO is the most practical method for removing silica from water supplies. It can reduce reactive and colloidal silica. It is important to note that you will need proper pretreatment. This will include removal of chlorine and chloramine, oxidation of manganese, sulfur, and iron, and water hardness treatments such as water softening. This will help maintain the integrity of the membrane and avoid the need for premature replacement.
It is also a good idea to incorporate a permeate flush into your RO system. This will mean the membrane is soaked with RO water, preventing scale from fouling the surface of the membrane.
While small quantities of silica are not thought to pose a threat to health, having silica contaminated water can create problems around your home. Like hard water minerals, silica can create scale that can impact the performance of your water using appliances and fixtures. It can also lead to unsightly stains around your home. So, if you suspect you have silica in your water, you should speak to a water quality specialist for further advice.