I'm in TX and we get some pretty darn strong sunshine here.
I'll also use a physical filter (likely mesh netting & paper liner) when pumping into the initial reservoir from the house. I forgot to mention that, as it is particularly useful re: water from the kitchen.
I am planning toward constructed / installed units, not a pond or ground level pool of some kind. I am thinking basic 2x4 and plywood or aluminum legs & plywood with window frames & glass tops secured on an angled orientation, in series or parallel.
I might put a black hose or copper line solar water heater in front of the stills to increase temperature and therefore minimize time in the stills. And of course the storage tanks themselves would be painted black to absorb as much heat as possible.
I want to move the water to these solar still units as quickly as possible, as grey water can begin to have issues at ~24 hours. If I tried going to the bio sand first, I'd have to have a TON more sand filters due to the slower rate of flow they can handle vs the stills. The 5 gallon bucket version of the bio sand filter I built would only handle 3-5 gallons in 1 hour. That's ~120 gallons per day, max. The 55 gallon version would handle more, but not by much more because the goal is to not disturb the sand and allow the bacterial layer to work unmolested. Area, not volume is the determining factor.
Plus, the bio sand drums will be WAY heavier and a logistical nightmare to move, so I'd like to keep those to a minimum. Also, this way the majority of suspended particles will get dealt with via paper filtration, high heat then evaporation vs clogging up the bio sand filter. And it's certainly a LOT easier to clean the stills than the filter sand.
The point of this effort is to clean the water from the site wells so it can be re-used for ANY purpose at the site. I can legally just disperse the grey water throughout the property as long as this is outside city jurisdictions. But to use slightly soapy / oily / bacteria contaminated water that way will only invite problems in general, let alone for anything consumption related. The RO method is FAR more expensive for such capacities AND requires much more energy.
The biggest $$$ for any household would be watering the lawn, just in sheer number of gallons required. But, if I could direct nearly all the 300-400 gallons used inside the house to be re-used again outside without real reservations, that would be a BIG win. Especially for vegetable gardening, etc.
The common US residential lot size is 8,600 sq ft or 1/5 acre. Subtract the average home itself and you have 6,000 sq ft that might normally be grass (leaving out the driveway anyway). That would require 3720 gallons per week just to water the grass. Which is essentially identical to the tomatoes. So even with a household of 4 people estimated at 400 gallons per day - you can just barely cover 2800 gallons per week of water recovered, no loss best case. So watering the lawn isn't really a viable option even with a SMALL lawn. Maybe with 6 people in the family and increased water usage that comes with the size, but then there's no water for anything else either.
Here in TX, beginning in May the sun can be so intense that tomato plants easily die within 1-2 days. The same is true for many edibles. If I could water them with purified water I have already paid for & used, I can water them daily without any extra cost aside from the passive equipment & one or two reasonably small pumps.
Tomato plants need 1 to 1.5 inches of water per week. In a raised bed garden 8' x 4' that is ~30 gallons a week. This plan would allow for 10x that size - or 320 sq ft of tomato plants, and allow for 6 more plants at the same area needed if it has similar water needs. Cucumbers, water melon, squash, or even corn could be grown very effectively in large quantities with that amount of water on hand. Some plants need more water. Corn is +50% over grass/tomatoes, and watermelon is +100%.
During the winter, we'd certainly have a surplus of water that we don't need. That's when we should consider a stock tank type situation. It's a lot cheaper to dig a hole in the ground than to buy three 10,000 gallon tanks at $5k each. At say 2,000 gallons per week, we would max out capacity on a $5k tank in 5 weeks. Since winter is 3-4 months, we'd need 12-16 week of capacity while the water isn't being used. Paying to store potable water is one thing, but I certainly don't want to pay $15k for water storage that is destined for veggies or animals, let alone flowers or grass. Even if the storage tanks last 15 years, that's $1k per year - far more than the water would cost.
So, given say 2 acres of space, there would be PLENTY of room for such an array of solar stills. Normal atmospheric evaporation rates I have found to be 1 gallon per square foot of area per hour for many municipalities. That's a far cry from the amount typically collected by stills, so there is large loss to the atmosphere to be sure. To handle ~300 gallons by assuming 2 gallons generated per day for each 1 square meter / 10.7 sq feet - I'd need 150 individual stills or roughly 50 8' x 4' stills. That's just bigger than 7 x 7 tables which would be 56' x 28' with no spacing in between.
Assuming the supplies expenses would be:
- Seven 96" 2x4 for main compartment & support (assuming 2' off the ground) $15
- One 96" x 48" plywood $25
- Plenty of PVC or similar pipe $10
- Aluminum flashing / fin material
- Labor to assemble
- Recycled window glass from remodels etc (free)
Then the silicon
- Black waterproof silicon roof rubber paint 5 gallons = 250 sq ft (good for 8 stills) @ $200 each
- Clear silicon to seal glass (4 case @ $25 = $100)
I am ball-parking $80-$100 per table with hardware.
For $5,000 one-time cost, with occasional maintenance costs on top of that, plus a few pumps & other hardware, I can handle throughput of 300 gallons through this system. Each table handles 6 gallons per day, assuming just 5 hours solid sunshine according to the various research I have read. Automating it will cost a bit more with sensors for water flow etc.
It seems if you have the space, this is a no-brainer. Call it $7k for everything, being overly conservative. $7k would pay for 700,000 gallons of water at $0.01 each. In one year, a typical family uses 109,500 gallons at a cost of $1095. So that's around 7 years of water I'd be paying for. Even then well water is generally FAR less per gallon, but you likely had to pay much more for the deep well to keep it that way. This plan would provide me with ~219,000 gallons per year, essentially doubling my available water at the same cost. Yes, if I want to get 100% of those gallons I need some storage for portions of the year, but the self-sufficiency alone is worth $$$ too.
To compare, rainwater harvesting on a 65' x 40' roof (front & back gutters) would generate ~55,000 gallons per year in my neck of the woods. It gets half the water over the same period as the grey purification concept. And when rural and/or in a drought that well water might need to be the main source of potable water, let alone used for anything else. This has been a real problem in TX in the past 5-10 years.
Drilling a well - say $15,000, more for deeper etc. Harvest rainwater - say $2000 before storage and it is certainly not potable at that point. This plan seems to fall easily between those, could potentially share the fresh water storage costs, and makes FAR more use of the water.