Suspended solids fall into two categories: turbidity and sediment. Turbidity refers to larger solids (such as leaves, spiders and frogs!) while sediment can be sand, silt or rust. Either way, all of the above can be removed by mechanical filtration.
It must be assumed that all private water supplies are potential sources of bacteria. Fortunately this issue is easily solved by using an ultra violet sterilisation unit. The location and flow rate through a U.V. unit should be planned before installation and the unit should be situated so that feed-water cannot be re-contaminated after treatment has taken place (i.e. in a storage tank).
All rainwater is slightly acidic and this acidity increases as the water passed through the atmosphere and through peaty soils. The lower limit for drinking water is pH 6.5, however at any level below pH7 water is deemed aggressively acidic in nature. Water below this pH will slowly dissolve pipework leading to blue staining and perforations and leading to a reduced lifespan for any water appliances. Drinking water with this level of acidity will sometimes have an astringent taste.
Acidic feed-water can be neutralised by passage through a single vessel containing dolomitic limestone. The vessel is backwashed to remove solids and should be checked annually as the media becomes depleted during the neutralising process. pH correction should be fitted at a location where all incoming feed-water will be treated.
Iron / Manganese Content
Some waters which are drawn clear develop an orange or brown colour soon afterwards. This is a sure sign that iron and / or manganese are present in the water as both these contaminants, once oxidised through contact with air, will form orange or brown deposits. While not being an immediate health risk they can give rise to unpleasant tastes and staining of laundry, sanitary ware and cutlery.
Due to the complicated nature of treatment for this issue, the type and level of iron must be analysed before treatment is attempted. Treatment systems for the removal of iron / manganese are often used in conjunction with other systems such as pH correction and ultra violet sterilisers.
Arsenic can leach from rocks and can be found in water supplies throughout the UK – it is poisonous (being a known carcinogen) and can cause skin and liver disorders and circulatory issues. The EU recently lowered the maximum admissible concentration (MAC) for arsenic down from 50ug/l to 10ug/l.
Aqua Cure Scotland can offer treatment systems for the removal of arsenic, including point of use ion exchange and reverse osmosis in addition to a range of fully automatic backwashing vessels for point of entry applications. Arsenic reduction vessels (ARV’s) contain a media called ferric hydroxide which has a capacity for arsenic (III) and arsenic (V). ARV’s can be used in conjunction will other treatment vessels, for contaminants such as iron / manganese, turbidity and pH correction vessels.
Yellow discolouration of water can be caused by organic compounds called tannins. These are usually found in peaty areas and in water supplies that are affected by surface water. Apart from discolouration, organic compounds can render water unfit for consumption and can foul filtration and reverse osmosis systems.
Although carbon filters can be used to remove organics, the media quickly becomes fouled when the organic load is high. Tannex filters consist of a mix of two organic resins which have a special porous structure designed to capture organic tannins. The resins are regenerated using sodium chloride brine, meaning the filter operates in a similar way to a softener, with a periodic backwash and regeneration.
The use of fertilisers in farming has been widespread for many decades and with this increase, the incidence of nitrate pollution has also risen. 55% of councils who responded to a survey on the subject indicated that nitrates were a major problem in their area. Shallow wells and boreholes suffer more than any other type of supply.
While not being easy to remove, there are a number of systems available to combat nitrates. Some rely on base exchange (nitrates are swapped for chloride) while others use reverse osmosis (a form of molecular separation).
Hard water is caused by dissolved calcium and magnesium salts in a water supply. Though eastern and southern areas of the UK suffer more with water hardness, there are some notable exceptions to this rule throughout the country.
Hardness is not directly harmful to health but hard water can precipitate (or release) the calcium / magnesium salts which stick to surfaces in the form of lime scale. This can cause blockages in pipework and can scale up heaters and kettles.
The standard way to treat hardness is to swap the calcium / magnesium for sodium using a water softener. the drinking of softened water should be avoided and people with a softener should fit a reverse osmosis purifier to remove the sodium from their drinking water.