Effect of sodium and phosphates on plant life

Can anybody help me with some information on this topic?

South Africa is facing a severe water crisis, with Cape Town's restrictions
presently at use of a hand held hose for 30 minutes per week, which will
give about a total of 150 gallons per week for the entire garden! Clearly a
garden cannot survive on this.

Despite this, households use between 5,000 and 10,000 gallons per month for
bathing, showering, clothes washing etc. We want to use this water in our
gardens, but many people are uncertain of the effect of the soap in the
water in the garden. Two major concerns appear to be the effect of
phosphates from certain washing powders, which does not make complete sense
since lawns often require additional phosphate to grow properly. Could a few
hundred grams of phosphate per month on a lawn covering 100 x 50 feet cause
severe damage? Would the phosphates not filter into the soil and be washed
away naturally?

Then you have the bio-degradable powders, with high levels of sodium (about
50 grams per wash) and other salts which "experts" claim will cause harm to
plants?

How much of this is true, and what do we do? Dilute the washing water
further, treat the water or garden to counter the effect of these salts and
phosphates, or let our gardens die and live in a desert?

Any thoughts? Much appreciated

Alan

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