OFF-GRID CLEAN WATER HOLDING TANK
Image courtesy of Plastic-Mart
Water obtained from the rain water catchment system intended for daily consumption and general use will be filtered through sediment & carbon block filters, then stored in a 50 - 55 gallon (FDA Regulation 21 CFR 177.1520 (1) 3.1 & 3.2) approved-food grade, BPA free, virgin polyethylene resin flat bottom seamless container. Management of this Clean Water Holding Tank includes, but is not limited to, maintaining water temperature and monitoring for microbiology.
The material the holding tank is made of is designed to hold “filtered” water. If a tank made of nonfood grade materials was used, the purity of Distilled, Deionization, Demineralized and especially Reverse Osmosis water would cause permeation and/or leaching of the holding tank.
The walls of the holding tank must be thick enough to avoid bulging at the sides when full; along with baffles to prevent sloshing of the water inside. The holding tank installation size will be determined on an estimation of what the daily consumption and general use will be for one to two occupants. The holding tank will have the ability to hold a max of 55 gallons of filtered water at 458.7 lbs / 208.6 kg at 62°F (17°C) when full; (1 Gal = 8.34 lbs/1.51 kg). The tank will be designed with DoT regulated transport applications; although capable, transport when full may not be recommended due to the added trailer weight during transport and fuel cost for the transport vehicle. The seamless holding tank will be elevated off the ground resting on a platform to facilitate access to the bottom of the tank for visual assessments of leaks or installation of a water leak sensor. The tank will be secured using 2 powder coated 2” steel bands.
WATER LEVEL MONITORING
The volume levels of the clean water holding tank can be measured using the Garnet Industries, SeeLevel II Holding Tank Monitor. Each SeeLevel II Tank Monitor is comprised of a Display (P/N 709-N2K-NLP)* and the Sender(s). The Sender is “a flexible self-adhesive printed circuit board which is adhered to the flat-straight side of the holding tank.” The Sender sensors are not compatible with metal tanks.
*N2K is shorthand for NMEA 2000 which is the communications standard used in the maritime industry for connecting equipment within the vessel.
The Display receives information from the Sender(s) via a single conductor. The tank volume is measured in percent of full on a 3 digit LED display. The tank volume is determined by detecting the dielectric difference between the air and water inside the tank. The Display obtains power from one positive (Red) conductor connected to a +12V source. The positive conductor has a 5 Amp Bussman 5 x 20mm GMA glass inline fuse. When purchased as an unassembled inline fuse holder, after assembly with an open barrel 20 - 18 Gauge terminal crimper, the potential for voltage drop or points of potential failure decreases by eliminating multiple splice points; along with a more professional appearance. A blue conductor sends signals to the Display while a black conductor serves as grounding. The Display is connected to the Victron Cerbo GX to enable remote monitoring of tank levels using Victron Remote Management (VRM) portal. A standard UTP/Network cable with RJ45 connectors transmit data between the Display and Cerbo GX.
The Senders are manufactured in various lengths: 12” P/N 709-RVC, up to 14” P/N 710-ES2. 2 Senders can be vertically stacked for longer lengths; up to 34” (Dual).
Image courtesy of Garnet Industries
The SeeLevel Sender is less invasive to install, requiring only a self-adhering adhesive found on the back of the Sender; unlike a rod like resistive tank sensor that requires making a perforation through the tank so the resistive sensor can be inserted.
WATER TEMPERATURE
The temperature, in the clean water holding tank, can be measured using an external Ruuvi Tag Pro (CR2477T). Inaddition to measuring water temperatures -40°F to 185°F (-40°C to 85°C), the Ruuvitag Pro also measures humidity & motion. Data can be monitored remotely when the Ruuvitag Pro is connected to the Victron Cerbo GX through the Victron Remote Monitoring (VRM) app.
The clean water held in the holding tank is intended to maintain the same temperature as the ambient indoor temperature in the living space of the Tiny Off-Grid House. While the trailer floor & walls of the Water Treatment compartment are insulated with closed cell foam insulation and ZIP-R sheathing; a removable ZIP-R insulated wall panel will separate the Water Treatment compartment from the living space. Removable wall panels will unlatch allowing access to the tankless water heater, water holding tank, filters, Vega ManaBloc Manifold, water pump and Expansion Tank for assessment or repairs. In cases additional heat is required—to prevent the formation of ice inside the holding tank—an external holding tank heating pad will be used. The external tank heating pad will be adhered to the flat surface of the holding tank heating the water through conduction.
TANK HYGIENE
The water will be cleaned/filtered before entering the holding tank. Filtering the water may not mitigate the need for additional disinfection.
If the water quality decreases in microbiology, color or taste, the holding tank & PEX distribution lines should be drained, descaled with > 5% Acetic Acid white distilled Vinegar, cleaned with Castile soap and water, then disinfected with a 1/100 solution of Sodium Hypochlorite (Bleach) and water dwelled in the tank and distribution lines, then rinsed (Flush); respectively, multiple times until test strips reveal negative signs of disinfectant. All these cleaners are non-toxic and biodegradable.
Please share your thoughts or experiences in the Comments section below.
