Sensor platform for assessment of water usage patterns in informal settlements

Rapid urbanization has intensified pressures on global water systems, particularly impacting informal settlements. Understanding water usage patterns within these settlements is of importance for better addressing water scarcity issues. Current methods for gaining information about water within these settings tend to lack spatio-temporal granularity and miss complex patterns of behavior related to water usage. As a consequence, there is a shortage of the reliable quantitative measurements needed to improve water management processes and modeling. Here we introduce a low-cost sensing platform for water assessment in informal settlements. Households within these types of settlements, lacking water utility connections and piping, often use storage tanks and buckets to distribute, store, and consume water; hence, the platform consists of four distinct sensor modules that can be placed on these types of water infrastructure. Evaluated in controlled settings, the sensors prove to be reliable for measuring water quantity, quality, and usage. Field testing within an informal community in Mexico reveals that the system can comprehensively track multiple tank storage levels, assess water quality, and capture bucket usage patterns without disrupting a household’s common activities or infrastructure. Our validation shows the technique’s potential to improve water management in informal communities, while opening opportunities for enhancement of water-related research and policy making through combinations of top-down and bottom-up interventions.


Tank Sensor
The tank sensor is placed on the lid of a container.The flattest and most centered spot on the lid is chosen as an ideal location for the sensor.Some lids have tilt that will result in the sensor's accuracy decreasing.The sensor is adhered to the lid by using 3M TM VHB TM two sided adhesive patches.Before adhesion, the lid is cleaned with ethanol so as to avoid having any dust particles that will compromise adhesion.The adhesive is heated up with a lighter so as to vulcanize it to the containers lid.Once in place, we apply pressure with our hands for 20 seconds to secure adhesion and fit.

Bucket Sensor
The bucket sensor is placed on the side of a given bucket.Adhesion is carried out similar to the process described above for the tank sensor.The bucket's case has a curvature that allows the adhesive to increase the surface area that is in direct contact with the adhesive and the bucket.This enables devices to have good adhesion independent of bucket curvatures.Correct placement of the bucket sensor is critical for the device to detect bucket usage.For buckets with handles, we place the sensor on one of the two sides of the bucket that have parallel planes to the handle.

Quality Sensor
The quality sensor is left floating inside of the container once it has been assembled.The case has a lower cavity that is filled up with water to balance the center of gravity for the device.We first fill up this cavity with water using a syringe.We then seal the cavity with a rubber plug.You may reference a in Figure 1 in the manuscript to see the red plug and the cavity.We then tie a string line to the sensor that will allow us or the community to retrieve the device even when water is low on a given container.This line is attached to an external point of the container so that it is easily accessible.

Battery Life
A critical component for the success of the device is battery life.Longer battery lives, would reduce the mental burden on communities that having to charge or swap batteries can represent.This is also crucial for being able to gain insight into long-term behavioral patterns and statistics.The current implementation's off the shelve low-power electronics, low-power communication protocol (esp-now) and low data collection rates allow for extended battery life on the wireless sensing nodes.Our calculations show that, within lab conditions, a wireless sensor node with a 420mAh battery is able to sample at a frequency of two times per day for more than 12 months.Field deployments show that humidity and temperature conditions make it more challenging for theoretical and laboratory experiments to hold.Improvements on case design and the use of higher capacity batteries could greatly extend battery life in the field.

Database Architecture
The HomeHub sends information to a remote server with a PostgreSQL-based database.The database has a relational architecture.This architecture allows for a easy access to all of the information from sensors that are connected to a specific HomeHub.this allows for complete and direct queries when further analyzing the data.The database uses the HomeHub's Mac Address as a primary key for registering any device.This means that a sensor that is not registered to a specific HomeHub will not be allowed to upload information into the database.This helps to ensure that all sensors that are queried for the manuscript's results analysis are registered under the HomeHub that is installed at the specific location of interest.It is important to note that all information is securely stored and anonymized so as to preserve privacy of our study participants.

Structured Interview Questions
This survey questions can help researchers to inform sensor deployments and to better understand water infrastructure of a given household.For this publication, this survey was used to dimension the system, detect the key tanks to place sensors and determine some of the expected behaviors that could be interpreted from the data.This survey can be used as a template for any team that is interested in activating their own sensor system within real-life deployment scenarios.The survey has five different section.Each one focuses on a different aspect of the infrastructure.Note that the section that addresses qualitative information like costs and water consumption is prone to yield answers that might not be very accurate or biased.Those questions can be better addressed and complemented through the sensing system.We note that these survey was used in Mexico, cultural adaptation might be required if it is used in other regions around the world.

Section 1
• On which street or avenue is your house located?
• Between which streets?
• How many people live in your household?
• How many bathrooms are there?
• How many bedrooms are there?• How does the drainage (sanitation system) or drain of your house work?
a.You are connected to the public network b.It is connected to a septic tank or septic tank (biodigestor) c.It is connected to a pipe that will dump outside of the house d.It is connected to a pipe that dump to a river, lake, or sea.e.I don't have drainage • When you have to buy water pipes, how long does a pipe last in the dry season?(Specify pipe capacity) • When you have to buy water pipes, how long does a pipe last in summer?(Specify pipe capacity) • When you have to buy water pipes, how long does a pipe last in winter?(Specify pipe capacity) • On average, how many pipes do you buy per year?
• Tell us a little about how you usually use water.Select all the actions that match how you use water in your home.• How much does a water pipe cost on average?
• How much did a water pipe cost when you moved to this colony?
• How much is the most you have paid for a water pipe?
• Select the option that best describes your situation when buying water from a pipe: (select only one option) • What do you consider to be the biggest challenge you face regarding the issue of water?
• How do you think this challenge could be solved? 5/5 a. I collect the cold water from the shower and use it for something else b.I water my plants with a hose c.I water my plants in the morning or evening d.I place dishes under the pots so that the water does not drain out e. I collect the water with which I wash dishes or clothes and use it for something more f.I reuse the water where I sow vegetables g.I leave the shower open while I soap h.I turn off the faucet while brushing my teeth Other:• How do you use and reuse water?

• 5 •
a. I always buy a complete pipe for my house b.Sometimes I share a pipe with a neighbor c.I usually share a pipe with other neighbors d.I always share a pipe with other neighbors • If we add up what everyone living in their household earns in a year, how much of that is spent on paying for the water they consume in that year?a. more than half b. between half and one-quarter c. between one-quarter and 10 d. less than 10 • Do you think you have a lot to pay for the water you consume?be interested in learning new techniques to improve water availability in your home?What would be the main reason for making these changes?a. Save money b.Save water c.Facilitating my access to water 4/What would be a reason for you not to make these changes?a. Lack of money b.Lack of someone to help me install it c.Lack of interest