How much distilled water do you need per day?
This is the primary sizing variable. A single adult who drinks only distilled water consumes roughly 2 liters per day. The VEVOR 4L unit (3.5-3.8L usable output per 4-hour batch) covers one adult with one daily batch run. For two adults or for households that use distilled water for cooking as well as drinking, the 6L unit (5.5L usable output per batch) covers daily needs with one cycle. For labs, aquarium facilities, or households of four or more, the 30L-per-day automatic unit eliminates batch management entirely.
Manual batch vs automatic refill
The 4L and 6L VEVOR units are manual-batch: you fill the boiling pot with tap water, start the unit, collect the output after 4-5 hours, and clean the pot before the next batch. This requires approximately 5 minutes of attention at the start and end of each batch cycle. The 30L-per-day automatic unit connects to a standard kitchen tap via a supply line and refills and cycles automatically without user intervention beyond emptying the collection tank and periodic cleaning. If the inconvenience of daily batch management is a concern, the automatic unit at approximately $200 addresses it.
VOC post-filtration: do not skip the carbon sachet
Distillation boils water and condenses the steam -- but VOCs (volatile organic compounds) that boil below 100C will vaporize with the steam and re-condense in the collection vessel. For municipal tap water, the primary VOC concern is disinfection byproducts: trihalomethanes (chloroform, bromodichloromethane) and haloacetic acids produced when chlorine reacts with organic matter. The activated carbon post-filter sachet that VEVOR includes in the collection vessel adsorbs these compounds before they reach the output. Do not skip the carbon sachet for municipal tap water use. Replace the sachet every 4-6 batches or when it shows discoloration.
When VEVOR is the right choice -- and when it is not
VEVOR is the right choice for: buyers evaluating home distillation before committing $200+ to a Megahome or WaterWise unit; aquarium hobbyists who need large volumes of low-TDS water for sensitive reef tanks; humidifier users who want to eliminate mineral dust from ultrasonic humidifiers; battery maintenance and automotive applications. VEVOR is not the right choice for: buyers who want laboratory-grade purity documentation (Megahome and WaterWise publish third-party purity data; VEVOR does not), buyers who run the unit 12+ hours per day (VEVOR cooling fans are rated for residential not continuous commercial duty), or buyers who want a glass collection vessel (VEVOR ships with plastic -- glass is available from Megahome).
Water hardness and VEVOR performance
Hard water (high calcium and magnesium content, above 120 mg/L or 7 GPG) will cause faster mineral scale buildup in the VEVOR boiling pot. In very hard water areas (above 20 GPG), the pot may need descaling after every 3-5 batches. Use a citric acid solution (1 tablespoon per quart of water, run a short heat cycle) to dissolve scale without abrasive scrubbing that damages the stainless surface. Soft water from an upstream whole-home softener reduces scale buildup significantly and extends cleaning intervals to every 10-15 batches.