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Building a Rainwater Filter for an Off-Grid Campervan

In the last article, we explored the feasibility of a rainwater collection system that could be mounted to the roof of a campervan in the interest of developing an ancillary off-grid water supply. In this article, we will be exploring the factors that can influence the safe operation of rainwater collection systems and the processes that can make clean water accessible without solely relying on mains infrastructure.

In this regard, we need to identify the types of rainwater contaminants and assess the effectiveness of different processing methods in the interest of creating a reliable water supply. Living and working in remote locations can make clean water less accessible, especially in locations that have unreliable mains infrastructure, so investing in these systems can be of benefit to your long-term health and touring potential while on the road.

Parts List

  • Filter housing (738-2716)
  • Filter cartridge (738-2712)
  • Self-regulating water pump
  • ½” BSP to ¾” BSP flexible hose
  • ¾” BSP to 15mm flexible hose
  • 15mm pipe
  • Ball valve

Understanding Water Contamination

Water is known as the universal solvent in many environmental circles and is a large part of the reason why man-made pollution is not significantly more noticeable. The water cycle helps clean the earth and the atmosphere by washing away any pollutants through native waterways. This makes collecting clean water more difficult in developing and developed nations without a level of processing or filtering first. These contaminants can generally be classified by their composition and can include:

Physical contaminants like dirt, dust and other particulate matter which can often cause cloudiness in otherwise clear water. These components can also include plastic and other physical waste that has broken down to the microscopic level and has the potential to be quite toxic.

Chemical contaminants are elements or compounds. These can be naturally occurring or man-made and can include industrial and agricultural runoff, minerals from soil erosion, infrastructure drainage, sanitation overflow and heavy metals like lead.

Biological contaminants are microorganisms suspended in water that include bacteria, viruses, fungi and parasites that can be quite dangerous in cases like e-coli.

Do you know what’s in your drinking water?

Do you know what’s in your drinking water?

Having an awareness of these contaminants will inform a safe and effective design for the rainwater capture and storage system used in our off-grid living environment. Fortunately, the majority of these contaminants affect groundwater, which can be avoided by collecting water as rain before it hits the earth. According to the World Health Organisation “rainwater is relatively free from impurities except those picked up by rain from the atmosphere, but the quality of rainwater may deteriorate during harvesting, storage and household use.” Therefore, the risks posed by these contaminants can be attributed mainly to the collection system itself and the local air quality during operation.

Keeping the collector clean

Keeping the collector clean

In the context of our campervan project, we can mitigate the risk of these contaminants by monitoring the local air quality and ensuring our capture and storage mediums are clean before use. Further precautions can be taken by installing gutter guards and water strainers to remove large debris while making use of our detachable hose to manually discard the majority of contaminants found during the initial period of rainfall. This initial filtering process is called the first flush and can significantly improve water quality as the bulk of contamination from air pollution and any surface run-off is not collected.

Automated first flush device

Automated first flush devices are very common

The first flush is capable of minimising all types of rainwater contaminants and is therefore important, but not perfect in removing these impurities. Further processing and filtering are required in the search for clean water which can be categorised by their respective functions:

Pasteurising and Sterilising involves either disabling or killing harmful organisms that can populate untreated rainwater. This is normally achieved through boiling or exposure to UV light that damages the cell structure of any harmful pathogens enough to become harmless.

Disinfecting involves the use of chemicals like chlorine that are added to the water in an effort to destroy harmful organisms. This method is used in mains water infrastructure but is not always as effective in neutralising all pathogens.

Distilling involves the controlled evaporation and condensation of water molecules and can be one of the most effective methods in removing all types of contaminants from untreated water. However, it is often more energy-intensive with a lower yield than other, more passive methods.

Filtering involves the removal of foreign objects like dust and dirt from untreated water by forcing the fluid through a semi-permeable membrane. It is an effective first stage in the purification process but can depend on subsequent processing to remove other types of water contaminants.

Installing A Simple Sediment Filter

The initial design for our off-grid water system will include a 5um sediment filter that will remove the majority of particulates from the collected water. An electric pump powered by our leisure battery will then automatically push water through the filter at mains pressure to the endpoint in our system ready to be dispensed. Chemical contaminants will be negligible in any collected rainwater but it is worth noting that the disinfectants used in any supplementary mains water will conveniently pass through the filter.

Filter housing with 5um sediment cartridge

Filter housing with 5um sediment cartridge

In the last article, we installed the rainwater collector on the roof of the campervan and successfully tested its ability to collect water with the detachable hose. We now need to install the pump and sediment filter to the forward system and complete the foundation of our off-grid water supply.

Connecting the inlet hose to the water pump and pressurising the outlet ready for filtering

Connecting the inlet hose to the water pump and pressurising the outlet ready for filtering

Using the existing 1/2” barb hose connection we can connect the water supply to the pump that will automatically regulate the pressure to 2 bar or 30 PSI which is the same as mains pressure and what needs to be supplied to the filter.

Powering the water pump using the leisure battery from our renewable array

Powering the water pump using the leisure battery from our renewable array

We can supply the pump with a constant 12v source from the same leisure battery that is being charged from our solar panels. The pump is designed to automatically regulate the outgoing pressure to the water system and so should not present a constant drain on our electric storage system.

Using a braided hose to connect the filter to the water pump input and the tap output

Using a braided hose to connect the filter to the water pump input and the tap output

Using a steel braided hose, we can connect the 1/2” BSP pump outlet to the 3/4” BSP inlet of the filter and use a similar hose to connect the filter to the tap outlet.

Fully assembled sediment filtration system

The fully assembled system is now ready to harvest rainwater from the roof of the campervan in preparation for our forward system to pump through and process on demand. The sediment filter is a good starting point for our clean water system but is only effective against certain containments so there is still plenty more to explore in regard to the safe collection and processing of rainwater. The recommended filter replacement interval is every six months so it will be interesting to observe the condition of the filter after this time to assess its effectiveness at blocking contaminants to the forward system and how it might later be evolved to increase efficiency.

Visit the Kickstart Kamper landing page on DesignSpark

Visit the Kickstart Kamper official website

A keen maker and electronic engineer with a passion for the environment, renewables, alternative transport and anything off-grid. Man with a van and founder of the Kickstart Kamper sustainable campervan project. Grassroots Education Sustainability Ambassador. BrightSpark 2017. BEng.