Challenge calculation swimming area To calculate the size of the swimming area you have to find out the influence of the next subjects: - rainfall; - roof & pool surface; - evaporation; - household use; - remainder household; - garden botanica; - buffer. rianfall If you want to know how much rain falls in a country, there are many websites who will give you these information. e.g. https://klimaatinfo.nl/klimaat/frankrijk/ I have searched for a region and gave about 750 mm/y. roof & pool surface Now we can calculate how much water we have: 282 m 2 (surface) x 0,75 mm/y (rainfall), gives 211.500 liters/y. evaporation Because of the wind, the temperature, humidity and sun, the water will evaporate. To calculate I have found a site: https://www.lenntech.nl/calculators/verdamping.htm The evaporation is in mm/month of the surface of the swimming area and the regeneration area. I calculated it was an average of 5,84 mm/day. Later I found a site: https://dengarden.com/swimming-pools/Determine-Evaporation-Rate-for-Swimming-Pool who speaks of a ‘rule of thumb’. You loose a quarter of an inch of the surface a day. 2,54 cm/4 gives 6 mm a day. I can live with that. The swimming area and the regeneration area gives a total of 36 m 2 So the lost per year is 3.600 dm 2 x 0,06 dm/day x 365 days gives 78.840 liters/y. It means a lost of 37% in a year. So if this is the situation than you can use 211.500 -/- 78.840 = 132.660 liters/y. I calculated in normal circumstances that a person use 42.500 liter a year. It is just enough for 3,1 persons/y. I also calculated the evaporation with a swimming area of 8 x 11 m and the evaporation was almost 80%. But when you cover the swimming area (18m 2 ) the lost by evaporation will be 19% instead of 37%, and the enough for 4 p/y. So you can win a lot by covering the swimming area. household use Let us remind the use of the water at this moment. It is 116,44 liters/d. What can we reuse? remainder household purple items The purple items, 4%, it’s a loss and not reusable. There is the urine as a by-product and when you cook with water a part will be poured off. I’m not calculating so in practice it is an extra. grey items From these items I only have at this moment a question mark by ‘toilet small’. The rest is reusable, if you uses biodegradable products. It gives a saving of 75 liter/pp/d (65%). We have to find out which products these are and which criteria there are to connect it into the regeneration area. toilet: This item is more complex because of the different kind of solutions. (normal situation) There is the toilet and all goes on the septic or wastewater treatment plant. (alternatives) I’ve seen a toilet which burns the faeces (at this moment € 3.400/ € 2.400, Incolet). There is the compost-toilet, no water is used and perhaps uses it for the garden. There is a toilet which separate faeces from urine, and no water is used. The alternatives give a saving of 36 liter/day (31%). In this diagram you see some of the different options, in which nr 2 is the best outcome. A septic costs more than € 5.000. The burn-toilet costs at this moment € 2.400 and power. Of cause when the grey items are used like the shower 48,90 liter, the rest after using is not 48,90 liter. But it also will not be tens of liters. So lets say for all these items a total of 1 liter and and for the washing machine 1 liter, makes 2 liters lost a day. (For the calculation I use 2,33 liter is 2%.) garden botanica We do have an experimental vegetable garden of 60 cm x 120 cm ( 8 compartments of 30 x 30 cm) and we sprinkle it every day so that the surface is humid enough. But if it rains, we do nothing. We have not the faintest idea what a garden needs. I have calculated that we need 32 compartments to eat both a whole year. 32 x 30 cm x 30 cm gives 2,88 m 2 . We also want to culture herbs and fruit. Let’s say we need in the beginning 4 m 2 . So how much water does a vegetable garden needs? The first site wrote about 1 to 6 inch a week. It was the first indication but there was no explanation with it. We had to grow deeper. I found a site with calculations. https://perfect-vegetable-garden.com/water-garden-inch-per-week https://ucanr.edu/sites/scmg/files/185639.pdf On both sites your food garden needs 0,623 gallons per square feet per week in the summer. In spring or autumn it is half of it. https://bonnieplants.com/gardening/how-much-water-do-vegetables-need/ On this site they say that your garden needs 1 inch water per week, but with every 10° F above 60° F it is ½ inch extra. 60° F = 15° C. every 10° F is about 5,5° C. 1 inch is 2,54 cm I also investigated the evaporation in this case when it is not a pool but soil. But the answer gives a negative figure, so I keep it out of the calculation. In the picture you can see the calculation by 4 m 2 . For a whole year it needs 6009 liters and that is per day 16,5 liters. Summary So what does the investigation show? If we don’t reuse water with the roof 16 x 14m etc. than there is for 4 persons water. By 65% reuse it gives 11 persons who can live of it. When we use a composite toilet it gives 94% profit over 81 liter use. In the summary I used three examples to keep it clear,but it shows that you can win a lot. In our calculation there was a lot of roof surface. I have calculated it also for a roof of 10 x 6 m, then there is about 56.000 liter. It is worthwhile for people to investigate and create only a small pond with a regeneration area in the backyard or use a reservoir as a storage tank for grey water. Also I am aware that the costs of the water in my country is almost nothing. But I am also aware that the quality gets worse. buffer In the calculation you have to think about a buffer of water if you are only dependent of rain water. Imagine that it is warm and no rain for 2 month. In the summary you see that the pool has 172.080 liters. In the summer months (june/aug) the rain is about 8.500 liters and the other months about 16.000 liters. So the worst case is 2 month x 16.000 liter = 32.000 liters less of 172.080 liters is 140.080 liters.