We have had the water tested and it's pretty good as far as heavy metals go. There are some infrequent fish die offs and it's definitely very turgid with a lot of algae.
The soil content is likewise low in heay metals, but also low in fertility with a pH around 7.5 - we are adding organic compost and animal manure at the time of planting.
I'll go with defining organic in our context rather than speaking about Taiwan in general. It's a meditation and yoga retreat with an emphasis on sentient/yoga diets (no garlic,onion,egg,meat,mushrooms) and we have more than 10 people who live on the property, many volunteers who stay here and also many guests. It's not so realistic in this rural and agricultural environment to be overly demanding about organic purity. I want to do the best I practically can. We generate A LOT of food scraps and make hot compost, we use farm-grown mulch regularly - but it breaks down fast, we use farm-made enyzmes and liquid compost along with commercial organic fertilizers.
I absolutely agree about planting trees and shrubs around the perimeter of the garden.
So, in conclusion, my thoughts for now...
1. Adding a foam sheet around the river pump will help prevent contamination, but will be a nightmare to regularly access and clean.
2. I'm looking at in-line filters, but they also have to be easy to screw in and out and cope with high pressure
3. A slow sand filter appeals to me, but I'm concerned it's not practical with a 20,000L tank to top up and the pump costing quite a lot to run if I reduce the incoming pressure into the tank and thus take much longer to fill it. Ideas?
4. Gravity feeding water down into the 20,000L tank from our lotus pond. Easier to access and filter. Might need to install a float valve
It's not so realistic in this rural and agricultural environment to be overly demanding about organic purity. I want to do the best I practically can.