Rainwater Harvesting

There's no need to convince anyone here that harvesting your own rainwater isn't only the eco-friendly thing to do, but it's also cleaner, healthier and much tastier. We all do it (mostly because we don't have any other choice) and if you do it right, you'll never want to drink chemical-polluted municipal water again.

RHEENENDAL CLIMATE OVERVIEW

Do we get enough water?

It's all about storage.

It rains enough in Rheenendal that you should be able to manage with natural rainfall only. Even the morning dew will trickle your tank full. You just need to attend to a few things...

It's all about optimal collection and adequate storage. During rainy seasons, you need to collect and store for the drier months. Water stays fresh in tanks and reservoirs, if not exposed to sunlight, so don't worry about water standing for months.

Most homes will already be set up for rainwater harvesting when you move in, so you might just have to improve on the system, if necessary. The idea is to fill your reservoir (or main tank) from the overflow of a first-catch tank, in order to enjoy clean water. You can add a filter before entering your home and even dispense a bit of chlorine (the type suitable for potable water) in the reservoir, for some peace of mind. But a little roof dust and bird poo won't kill you.

Do this to benefit the most from your free, clean water supply from above:

01

Optimise Collection

Add gutters-to-tanks to every roof you have. Even your small car port roof can fill a tank, which can be used for the extras you don't want to waste your drinking water on. Link your loose standing tanks where possible, so that overflow waste doesn't happen and you store all run-off.

02

Maintain Gutters

Ensure that all your gutter connections are secure and that there are no leaks. A dripping gutter can waste more water than you'd imagine. Consider changing from PVC gutters to seamless aluminium gutters. Always keep gutters clean to ensure optimal water flow.

03

Use Conservatively

Encourage your household to use water conservatively. Even if you collect enough water, the rule of thumb is that you should have enough in storage to last you through three dry months. But should you run out, you can purchase water from the municipality (at a hefty cost).

Knysna municipality can send a 5 000 litre water tanker to fill your tanks / reservoirs.

Costs are calculated at ± R1 033,80 per tank (a little over 20c per litre for 5 000 litres), plus R24,61 per kilometre from the Knysna fire station to your property and back.

Do the calculation.

How much to store for how much you need.

Calculate your water usage (considering the number of family members and vast extra consumption if you offer guest accommodation).

Then calculate your roof space (catchment area) and storage capacity (litres of tanks and reservoirs).

Compare this to the average rainfall for our area to guestimate if you have enough storage capacity for your average needs – then add a little extra, in case.

According to ISO, South Africans use ± 235 litres of water per day. So, for a household of four, that equals almost 30 000 litres per month. Probably more if your kids generate loads of washing and bath daily.

Calculate your roof size. This is a flat square metre area, so just Wall 1's Length x Wall 2's Length. Do not measure the up and down areas of your roof's pitch – just measure it as if you have a flat roof.

1 m² of roof will catch 1 litre of water for 1 ml of rain. So, if your roof is 100 m² and it rains 10 mm, then you catch: 100 x 10 = 1 000 litres. A 250 m² roof fills a 5 000 litre tank when it rains 20 mm (250 x 20 = 5 000).

YEAR	JAN	FEB	MAR	APR	MAY	JUN	JUL	AUG	SEP	OCT	NOV	DEC	TOTAL ml
AVERAGE	73,82	62,76	81,93	73,58	58,78	59,96	64,26	74,56	62,32	94,81	91,39	74,68	859,14
2023	79	99	115	54	144,5	102	90	21	127,5	77,5
2022	13	58	93,5	65,5	56	107,5	46,5	68,5	46	48,5	8,5	79	690,5
2021	75,5	44	80	49,5	90,5	16	47,5	97,5	54	83,5	130,5	132	900,5
2020	138,5	60	64,5	64	69	18	30	52	47,5	98	116,5	61,5	819,5
2019	44,5	66	116	52,5	38,5	28,5	64	4,5	80	65	130	37	726,5
2018	132,5	53	92	51	31	34	37,5	62	134	56	166,5	51	900,5
2017	102,5	33	38	29	15,5	11,5	35,5	59,5	64	85	124,5	35	633
2016	68	51	107	77	30	62	54	42	118	20	31	45,5	705,5
2015	50,5	91	141	115	63	102	106	165	171	42	134	51	1 231,5
2014	187	76	84	178	44	37	38,5	44	65	63	118	92	1 026,5
2013	100	99	61	15	43	73	46	140	17	202	125	8	929
2012	21	60	83	59	32	92	264	109	15	212	54	44	1 045
2011	54	39,5	67	33	232	126	152	130	16	69	69	112	1 099,5
2010	66,5	51,5	17	67	29	125	88	36	25,5	105	68	123	801,5
2009	4,5	73	24	73	17	74	66,5	23	79	66,5	55	64	619,5
2008	74	77,5	39,5	25,5	8	56,5	29	53,5	42	95	82	23	605,5
2007	100	46,5	97	56	115	8	69	43	63	77	461	104	1 239,5
2006	59	42	89	87	81	38	64	363,5	28	85	28	57	1 021,5
2005	88	67	103	131	57	55	6	27,5	42	17	83	40	716,5
2004	62	75,5	105	62	53	52	42	52	108	76	33	263,5	984
2003	40,5	47	259,5	42	122	41	46	54	20	53	44	50	819
2002	48	42	20	61,5	30	90,5	101	89,5	111	20	68,5	76	758
2001	74	55,5	70	94	23	15,5	56,5	63	52	66	131	61,5	762
2000	118,5	132	132	33,5	14	18	20,5	16	50	72,5	114,5	127	848,5
1999	101	77,5	97	91,5	37,5	18	63	46,5	39,5	127	24,5	27,5	750,5
1998	74	44	101	21	74	25	61,5	86	44	58,5	75,5	92	756,5
1997	30,5	80	134	122	137	95	48	89	32,5	138	42,5	28	976,5
1996	59	44	45,5	28	26,5	22,5	74	58,5	59,5	256	292,5	118,5	1 084,5
1995	73,5	73,5	106	117	75	36	34	32	60	61	216,5	128,5	1 013
1994	75,5	78,5	66,5	109,25	30	33	87,5	129	44	136	35	148	972,25
1993	90	70,5	53	128,5	59,5	73	44	66,5	195	40,5	77,5	104	1 002
1992	54	91	62	62	58	190,5	150	164	37,5	219	127	22	1 237
1991	93	60	38	18	57	20	57	39	9	111	16	78	596
1990	71,5	84	41	93	65,5	113	6	57	50,5	109	93	31	814,5
1989	51	42	52	126	34	33	45	16,5	32,5	157	135	43	767
1988	42,5	35,5	112	53	45	41	55	43	41	57	46	63	634
1987	92	49	76	125	7	76	27	71	175	58	12	63,5	831,5
1986	70,5	50	49	28,5	11,5	20	48	131	48	130,5	42,5	43	672,5
1985	94	104	47	75	21,5	50	80	15	31,5	165,5	93	108	884,5
1984	46	40	83	20	24	31	74	17	31	106	43,5	83	598,5
1983	34	76,5	55,5	36	57	155	153	33	73	117,5	47,5	72	910
1982	58	52	89	262,5	0	94,5	13	0	114	96,5	50	48	877,5
1981	153	42,5	170	115	274	51	37	209,5	35,5	130	32,5	90	1 340
1980	66	28	29,5	76	30	85	28	55,5	75	94,5	110,5	126	804
1979				29	83	52,5	106,5	126,5	66	26	33	32	554,5

Average rainfall in Rheenendal calculated daily at 08:00 by Riana Barnard from Barnard Boerdery