Here in the UK, the regulations regarding non-potable water supplies are tied in with building regulations. That makes a lot of sense, because it is within the home or a commercial building that rainwater is generally collected and used. The legal instrument is the national building regulations and Water Supply (Water Fittings) Regulations 1999.
Key Principles
The key principle that the regulations promote and uphold is the total isolation of non-potable water from all drinking water supplies. Therefore they run in parallel with guidelines on how the mains water supply should be connected to a household or building, and what basic plumbing features must be adhered to.
Essentially, rainwater (or any other non-potable water) must be kept totally separate from mains water by means of an ‘air gap’. Non-return valves, check valves and motorised valves are not sufficient as undesirable organisms can ‘migrate’ through the valve. The inclusion of the air gap will therefore be the only method permitted so it is important that this is included in your system. If possible, the system should contain a WRAS-Approved mains water unit; this means that it has undergone independent rigorous testing and has been approved under the Water Regulations Advisory Scheme.
Obviously harvested rainwater should run through a totally separate set of pipes, use different and unconnected storage tanks, and all pipes and fitting must be clearly marked as being Not Drinking Water. The Environment Agency had published a useful short guide, which is still available here. Another useful source of information is the Water Regulations Advisory Scheme (WRAS).
Using Harvested Rainwater
Harvested rainwater is used for:
- Flushing toilets
- Laundry
- for washing the car or watering the garden
It is NOT used for:
- Drinking or cooking
- Washing dishes
- Bathing and personal hygiene
There are exceptional cases in remote areas where rainwater or groundwater may be utilised as the source of drinking water for a home. Usually this requires disinfection to ensure the water is suitable and safe. This is normally achieved using ultra violet light treatment (UV) to destroy any pathogens or microbial threats. Reverse osmosis (RO) may also sometimes be used.
In commercial buildings, untreated rainwater can also be used for a variety of other uses; cleaning, cooling, process water etc. (n.b. where water is to be used in a situation that may create an aerosol effect e.g. pressure washer, some form of disinfection such as UV should be included)
How The UK Rainwater Regulations Compare With Other Countries
Because of our historically plentiful rainfall here, UK authorities have generally been less concerned with promoting rainwater usage than, say, building flood defences and promoting flood prevention measures. That has made perfect sense for this part of the world. By contrast, most states in Australia have made it mandatory for all new builds to incorporate a rainwater tank for flushing toilets. Belgium too has introduced similar legislation that ensures new buildings must include a tank to catch rainwater as a way of alleviating flood risk; it is therefore a simple step to make use of this captured water.
Other countries have their own regulations, often at state level. That makes sense as New Mexico, for example, has a water starved climate compared with, say, New England or Vermont. In New Mexico, all commercial buildings must be capable by law of harvesting and storing rainfall from the roof, to be used for landscape irrigation.
With our changing climate, and the UK having seen the driest summer on record in 2018, there may be a growing incentive to consider a similar approach here, at least is some parts of the country.
Why Are These Regulations Necessary?
Rainwater that is collected and adequately filtered is clean and clear, so is quite sufficient for certain uses. However, it is important to recognise that it is not necessarily free from contaminants. Because it is collected from a roof surface via guttering and downpipes, it has plenty of opportunity to pick up a variety of micro-organisms. The main source of this will be from bird droppings, which are inevitably always present on any roof surface. There may also be insects, molluscs or small rodents which could cause contamination. Organisms such as E.coli, Shigella, Salmonella and Cryptospiridium are all potential hazards.
If rainwater were to come in to direct contact with a mains water pipe, bacteria and viruses could migrate and potentially contaminate the mains water supply. Whilst the likelihood of this happening is low, the regulations are there for a very good reason and should always be adhered to.
The Bottom Line
While the UK rainwater regulations are not onerous and represent nothing more than applied common sense, it is vital to observe them. Keeping harvested rainwater completely isolated from potable water supplies is nothing less than an important health and safety measure to prevent contamination.
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