What is Reverse Osmosis?
Reverse Osmosis (RO) is considered the highest standard for filtering water and the most effective way to remove uranium and arsenic and other contaminants like bacteria, pesticides, chloride, lead, and aqueous salts. [1] After passing through a RO system, the filtered water can be used as both drinking water and for agricultural purposes. This system would produce the best quality water for Navajo schools but there are some limitations that may prevent it from being implemented.
RO works by pre-filtering contaminated water (carbon and sediment filter or even water softener) before forcing it to pass through an ultrafine filter (as small as 0.0001 micrometers or 10,000 times smaller than the width of human hair) at a high pressure. These pore sizes only allow water molecules to pass through, with larger contaminants and microbes being blocked by the filter [2]. The resulting water can then be stored in a storage tank for instant access and may finally pass through a post filter to remove unwanted odors or taste [3]. For agricultural purposes, farmers can also later add different nutrients to the water due to the treated water removing all nutrients and contaminants. The subsequent re-adding of nutrients into water is beneficial to the growing process as contaminants in the initial water source like iron, manganese, calcium, magnesium, and chlorine can react with nutrients and ruin fertilizers [4].
Figure 1 represents how reverse osmosis works as contaminated water is pushed through an ultrafine filter [11]
Cost and Installation:
There are three main types of RO systems: point of use, point of entry, and commercial systems. Point of use RO systems filter water at a single tap, typically a sink faucet, to produce around 10 to 75 gallons [45-340 Liters] per day [5]. These systems can be slower than point of entry filtration systems with bulky attachments. The costs for point of use systems range from $150 to $1500 [for top-of-the-line models] with more expensive options being more water efficient [6]. Point of use systems can be installed without a professional technician with the assistance of tools like electric drills, screwdrivers, wrenches, hammers, and center punches. Installation and troubleshooting guides can easily be found online or with the purchased filtration system, including this one [7]. This system can be used if the school is low on funding or to demonstrate to students how to install RO systems. One additional thing to consider when installing the RO system is that the use of water softener is recommended to offset the higher cost of membrane replacement despite its slightly higher initial cost of installment. Also, it is recommended to use polyethylene tubing (~$1.67 per foot) as RO water corrodes copper and galvanized pipes, diminishing water purity and damaging pipes [8].
Figure 2 features a diagram of a point of use reverse osmosis system [7]
In contrast, point of entry RO systems filter water for entire homes or small schools at the point in which water enters the facility. It filters at faster rates than point of use systems, generating up to 200 gallons per day. This system is preferable if the school depends on well water or rain water as a source of water. This system is more capable than the point of use system for supplying all the water needed for agriculture and drinking purposes within the small school. However, it is more costly and requires a technician to be installed, costing around $750 to $7,500 depending on the size of the small school. Higher priced systems also tend to be more efficient at filtering, producing less wastewater. For larger schools, commercial systems that have higher capacities and can distribute water from multiple sources may be more preferable. These systems can range from $1,000 to $20,000 with an additional installation cost of $500 to $2,000 as the system cannot be installed without a technician or plumber [6].
| Type of RO System | Cost | Description | Technician Required? |
| Point of Use | $150 – $1500 | Filters at a single tap or faucet | Recommended |
| Point of Entry | $750 – $7,500 | Filters small facilities at point water enters facility | Required |
| Commercial System | $1,000 – $20,000 | Filters at large facilities at multiple sources, higher capacities for water storage | Required |
One limitation of RO includes its need for maintenance. It is recommended that pre-filters and posters are replaced every 12-18 months with the membrane replaced every 2-4 years. With proper maintenance, the RO system should be able to function for 10-15 years [1]. However, with limited access to hardware stores, Navajo Nation schools may struggle to get access to the specific materials and supplies needed to maintain or replace the filtration system. They may require funding or outside assistance to properly install and maintain this system. Additionally, the average cost for maintenance for a point of use RO system is $50 – $100 per year with higher costs for point of entry and commercial systems [6].
The biggest limitation regarding RO is the amount of wastewater it produces. On average, 4 gallons of water is needed to produce 1 gallon of filtered water [4]. Some inefficient systems can generate up to 10 gallons of wastewater per gallon produced [9]. The wastewater could be disposed of safely through a drain, but it could be recycled for household chores like cleaning dishes and for laundry pre-rinse [10]. This system may not be feasible if the Navajo Nation school does not have reliable access to a water source. RO systems with higher costs are more efficient at producing less wastewater but this decision depends on how much funding is available to the given school.
Works Cited:
[1] What is a reverse osmosis system and how does it work? | Culligan Water. (n.d.). Www.culliganwater.com. https://www.culliganwater.com/blog/what-is-a-reverse-osmosis-system-and-how-does-it-work.
[2] DBrower. (2021, January 27). How to Remove Uranium From Drinking Water. Earth Water Alliance. https://www.earthwateralliance.org/filtering-systems-for-uranium-and-radioactive-particles/.
[3] iSpring Water Systems. (2021, January 14). Reverse Osmosis Water Filtration System for Hydroponics and Vertical Farming. Www.123filter.com. https://www.123filter.com/ac/reverse-osmosis-water-filtration-system-for-hydroponics-and-vertical-farming.
[4] Grower 101: Reverse Osmosis -The Pros and Cons – Greenhouse Product News. (2016). Greenhouse Product News. https://gpnmag.com/article/grower-101-reverse-osmosis-pros-and-cons/.
[5] Reverse Osmosis System Buyer’s Guide | ESP Water Products. (n.d.). Www.espwaterproducts.com. https://www.espwaterproducts.com/reverse-osmosis-buyers-guide/#:~:text=A%20Reverse%20Osmosis%20system%20will.
[6] Crail, C. (2022, April 26). How Much Does A Reverse Osmosis System Cost. Forbes Home. https://www.forbes.com/home-improvement/home/reverse-osmosis-system-cost/.
[7] Reverse Osmosis System Installation Guide – H2O Distributors. (n.d.). Www.h2odistributors.com. https://www.h2odistributors.com/pages/manuals/reverse-osmosis-installation.asp.
[8] gpienta. (2021, May 27). What Is the Best Material for Reverse Osmosis Water for Hospital Equipment? ASPE Pipeline. https://www.aspe.org/pipeline/what-is-the-best-material-for-reverse-osmosis-water-for-hospital-equipment/.
[9] US EPA, O. (2022, January 7). Point-of-Use Reverse Osmosis Systems. Www.epa.gov. https://www.epa.gov/watersense/point-use-reverse-osmosis-systems#:~:text=For%20example%2C%20a%20typical%20point.
[10] The Truth About Reverse Osmosis Waste Water | American Home Water & Air. (2020). https://americanhomewater.com/the-truth-about-reverse-osmosis-waste-water/.
[11] What is Reverse Osmosis (RO)? – Working Principle & Benefits with FAQs. (n.d.). BYJUS. https://byjus.com/chemistry/reverse-osmosis/