Other health implications
Water tanks are close to houses. They usually contain water during some or all of any dry season, a time when alternative breeding grounds for mosquitoes dry up.
For both these reasons it is important that they do not act as significant breeding sites. The design of tanks and guttering to exclude insect breeding requires a mixture of common sense and professional engineering.
It is common sense to so align gutters, and keep them clear of blockages, that they do not hold stagnant pools after rainfall finishes. It is engineering expertise or long experience that generates good designs for self-clearing gutters or filters.
Mosquitoe eggs are sufficiently small that they could pass through most filters with entry water: such filters cannot be very fine if they are to be able to handle the sudden and large flows during intense tropical rainfall of up to 1millimetre per minute.
Mosquito control is therefore a matter of preventing the entry and exit of adult insects and interfering with larval growth. The former may be difficult to achieve if tank maintenance is poor or if users place greater importance on maximising tank inflow than on maintaining mosquito defences. It is therefore attractive to have larval control.
This may take the form of active control with fish predators, surface oil films and suchlike but a more rewarding general policy is to starve larvae. Maintaining darkness in a tank prevents photo-synthesis and the growth of algae. Preventing the entry of suspended materials reduces the general nutrient levels supporting any biological chain.
If a child falls into a tank, even if that child can swim, there is a real danger of drowning. Many existing tanks have no covers or easily displaced covers and stories of children deliberately bathing in free-standing RWH tanks are to beheard.
Perhaps of most concern are underground tanks whose covers have been opened for inspection, maintenance or even for drawing water. It is not normal to fence underground tanks, to extend them above the ground high enough todeter access by crawling babies or to socially control children from playing on them.
However fencing and/or partial raising could have advantages including reducing danger of contamination by surface water and lowering the chance of cover damage by vehicles as well as reducing the risk of children or night-moving adults falling in.
Accidents like drowning are most likely where a new technology is being introduced and therefore should be the particular concern of technology-change agents.
The wall around the underground tank shown on the picture below is definitely not high enough to prevent children from falling unto the corrugated iron roof - which itself might not be very stable!